In this javascript for Leaflet.js can you write a function that when called will increase the speed of the marker animation in the 'moveMarker();' and 'moveBackMarker();' functions by 20. - 'var money = 100000;
var numberOfCarriages = 1;
var speed = 60;

const map = L.map("map").setView([54.2231637, -1.9381623], 6);
// Add custom zoom control to the map with position set to ‘topright’
const customZoomControl = L.control.zoom({ position: "topright" }).addTo(map);

// Remove the default zoom control from the map
map.removeControl(map.zoomControl);

let clickedPoints = [];
let isLineDrawn = false;
let marker; // Declare the marker variable
let progress = 0;
// Function to create circle markers with click functionality
function createCircleMarkers(geojson) {
 return L.geoJSON(geojson, {
  pointToLayer: function (feature, latlng) {
   const circleMarker = L.circleMarker(latlng, {
    radius: 4,
    fillColor: "#ff7800",
    color: "#000",
    weight: 0.2,
    opacity: 1,
    fillOpacity: 0.8,
   });

   // Attach the feature to the circle marker
   circleMarker.feature = feature;

   circleMarker.on("mouseover", function () {
    this.bindPopup(feature.properties.city).openPopup();
   });

   circleMarker.on("click", function (e) {
    if (!isLineDrawn) {
     clickedPoints.push(e.target); // Push the circle marker with attached feature

     if (clickedPoints.length === 2) {
      const firstCityCoords =
       clickedPoints[0].feature.geometry.coordinates;
      const secondCityCoords =
       clickedPoints[1].feature.geometry.coordinates;

      const polyline = L.polyline(
       clickedPoints.map((p) => p.getLatLng())
      ).addTo(map);

      const firstCity = clickedPoints[0].feature.properties.city;
      const secondCity = clickedPoints[1].feature.properties.city;

      clickedPoints = [];
      isLineDrawn = true;

      // Remove click event listener after a line has been drawn
      map.off("click");
      // Set the map bounds to show the area with the polyline
      map.fitBounds(polyline.getBounds());
      money = money - 50000; // Subtract 50000 from money
      const moneyDisplay = document.getElementById("moneydisplay");
      const moneyString = `£${money}`; // Assuming money is a number
      moneyDisplay.textContent = moneyString;

      const instructionsElement = document.getElementById("instructions");

      // Clear any existing content in the instructions element:
      instructionsElement.innerHTML = "";

      // Create separate paragraph elements:
      const congratulationsParagraph = document.createElement("p");
      congratulationsParagraph.textContent = `Congratulations you have built your first train line from ${firstCity} to ${secondCity}!`;

      const costsParagraph = document.createElement("p");
      costsParagraph.textContent = `Your construction costs were £50,000. You have £50,000 remaining.`;

      const buyTrainParagraph = document.createElement("p");
      buyTrainParagraph.textContent = "You now need to buy a train.";
      const newTrainParagraph = document.createElement("p");
      newTrainParagraph.textContent =
       "At this time you can only afford to buy the train engine the Sleeping Lion. The Sleeping Lion has a traveling speed of 60 miles per hour. It can pull four carriages. Which means your train will have a capacity of around 120 seated passengers";
      const traincost = document.createElement("p");
      traincost.textContent = `The Sleeping Lion will cost you £30,000 to purchase. Do you wish to buy the Sleeping Lion?`;

      // Append paragraphs to the instructions element:
      instructionsElement.appendChild(congratulationsParagraph);
      instructionsElement.appendChild(costsParagraph);
      instructionsElement.appendChild(buyTrainParagraph);
      instructionsElement.appendChild(newTrainParagraph);
      instructionsElement.appendChild(traincost);

      // Add button element:
      const buyButton = document.createElement("button");
      buyButton.id = "buybutton";
      buyButton.textContent = "Buy Train";

      // Append the button element to the instructions element:
      instructionsElement.appendChild(buyButton);

      // Add click event listener to the Buy Train button
      document
       .getElementById("buybutton")
       .addEventListener("click", function () {
        money = money - 30000; // Subtract 30000 from money
        const moneyDisplay = document.getElementById("moneydisplay");
        const moneyString = `£${money}`;
        moneyDisplay.textContent = moneyString;
        // Update instructions content after successful purchase
        instructionsElement.innerHTML = ""; // Clear previous content

        const successMessage = document.createElement("p");
        successMessage.textContent = `You now have a train line from ${firstCity} to ${secondCity} and a train! Press the button below to begin operations.`;
        instructionsElement.appendChild(successMessage);

        // Add button element:
        const trainButton = document.createElement("button");
        trainButton.id = "trainbutton";
        trainButton.textContent = "Start Train";

        // Append the button element to the instructions element:
        instructionsElement.appendChild(trainButton);

        // trainButton click event listener:
        trainButton.addEventListener("click", function () {
         // Clear any existing content in the instructions element:
         instructionsElement.innerHTML = "";

         const networkMessage = document.createElement("p");
         networkMessage.textContent = `The ${firstCity} to ${secondCity} Rail Company is in operation!`;

         const scoreMessage = document.createElement("p");
         scoreMessage.textContent = `You will now earn money every time your train arrives at a station (depending on the number of passengers on board). You do not need to worry about scheduling. Your train will now automatically run between your two stations.`;

         const updatesMessage = document.createElement("p");
         updatesMessage.textContent = `As you earn money you can invest in improving the ${firstCity} to ${secondCity} Rail Company. At the moment your train only has one passenger carriage. Why not increase how much money you make by buying more carriages? Each carriage will cost £20,000.`;

         instructionsElement.appendChild(networkMessage);
         instructionsElement.appendChild(scoreMessage);
         instructionsElement.appendChild(updatesMessage);

         // Get a reference to the div element with id "menu"
         const menuDiv = document.getElementById("menu");

         // Create a new image element
         const image = new Image();

         // Set the image source URL
         image.src =
          "https://cdn.glitch.global/df81759e-a135-4f89-a809-685667ca62db/carriage.png?v=1712498925908";

         // Optionally set the image alt text (for accessibility)
         image.alt = "add carriages";

         // Set image size using inline styles
         image.style.width = "60px";
         image.style.height = "60px";

         // Append the image element to the div
         menuDiv.appendChild(image);
         // Attach a mouseover event listener to the image
         image.addEventListener("mouseover", () => {
          image.style.cursor = "pointer";
         });
         // Attach a click event listener to the image
         image.addEventListener("click", () => {
          console.log("Image clicked!");

          // Check if enough money is available
          if (money >= 20000) {
           // Check if maximum number of carriages reached
           if (numberOfCarriages < 4) {
            numberOfCarriages++;
            money -= 20000; // Subtract 20000 from money

            const moneyDisplay =
             document.getElementById("moneydisplay");
            const moneyString = `£${money}`;
            moneyDisplay.textContent = moneyString;

            // Update instructions content after successful purchase
            instructionsElement.innerHTML = ""; // Clear previous content

            const newcarriageMessage = document.createElement("p");
            newcarriageMessage.textContent = `Congratualtions you have bought a new passnger carriage. You now have ${numberOfCarriages} passenger carriages.`;

            instructionsElement.appendChild(newcarriageMessage);

            // Create a new image element for the train
            const newTrainImage = new Image();
            newTrainImage.src =
             "https://cdn.glitch.global/df81759e-a135-4f89-a809-685667ca62db/train.png?v=1712498933227";
            newTrainImage.alt = "Train Carriage";
            newTrainImage.style.width = "60px"; // Adjust size as needed

            newTrainImage.style.height = "60px"; // Adjust size as needed

            // Attach a click event listener to the newTrainImage
            newTrainImage.addEventListener("click", () => {
             console.log("Train icon clicked!");
             instructionsElement.innerHTML = ""; // Clear previous content

             const improveBoilerButton =
              document.createElement("button");
             improveBoilerButton.textContent =
              "Improve Boiler for £2500"; // Add functionality to the button (optional)

             improveBoilerButton.addEventListener("click", () => {
 if (money >= 2500) {
 // Update speed and calculate new latStep and lngStep values for moveMarker
  const speedIncrease = 20;
  money -= 2500;
  speed += speedIncrease;
  const distance = firstPoint.distanceTo(secondPoint);
  const steps = ((distance / speed) * 1000) / intervalDuration;
  const latStep = (secondPoint.lat - firstPoint.lat) / steps;
  const lngStep = (secondPoint.lng - firstPoint.lng) / steps;

  // Calculate new latStep and lngStep values for moveBackMarker
  const latStepBack = (firstPoint.lat - secondPoint.lat) / steps;
  const lngStepBack = (firstPoint.lng - secondPoint.lng) / steps;

  // Update money display immediately
  const moneyDisplay = document.getElementById('moneydisplay');
  const moneyString = `£${money}`;
  moneyDisplay.textContent = moneyString;

  // Restart both animations with the updated speed
  moveMarker(); // Restart the forward animation
  moveBackMarker(); // Restart the backward animation
 } else {
  console.log("Insufficient funds! You need £2500 to improve the boiler.");
   instructionsElement.innerHTML = ""; // Clear previous content

           // ... insufficient funds logic ...
           const fundsMessage = document.createElement("p");
           fundsMessage.textContent = `Insufficient funds!`;

           instructionsElement.appendChild(fundsMessage);
           
 }
});

             instructionsElement.appendChild(improveBoilerButton);
            });

            newTrainImage.addEventListener("mouseover", () => {
             newTrainImage.style.cursor = "pointer";
            });

            // Append the new train image to the menu element
            const menuDiv = document.getElementById("menu");
            menuDiv.appendChild(newTrainImage);
           } else {
            console.log(
             "Maximum number of carriages reached! You can't buy more."
            );
            instructionsElement.innerHTML = ""; // Clear previous content

            const maxCarriageMessage = document.createElement("p");
            maxCarriageMessage.textContent =
             "You already have the maximum number of carriages (4).";
            instructionsElement.appendChild(maxCarriageMessage);
           }
          } else {
           console.log(
            "Insufficient funds! You need £20,000 to buy a carriage."
             // ... insufficient funds logic ...
           );
           instructionsElement.innerHTML = ""; // Clear previous content

           // ... insufficient funds logic ...
           const nomoneyMessage = document.createElement("p");
           nomoneyMessage.textContent = `Insufficient funds! You need £20,000 to buy a carriage.`;

           instructionsElement.appendChild(nomoneyMessage);
          }
         });

         const firstPoint = L.latLng(
          firstCityCoords[1],
          firstCityCoords[0]
         );
         const secondPoint = L.latLng(
          secondCityCoords[1],
          secondCityCoords[0]
         );

         const intervalDuration = 10; // milliseconds per frame
         const distance = firstPoint.distanceTo(secondPoint);
         const steps = ((distance / speed) * 1000) / intervalDuration; // Assuming speed of 35 miles per hour
         const latStep = (secondPoint.lat - firstPoint.lat) / steps;
         const lngStep = (secondPoint.lng - firstPoint.lng) / steps;

         // Create the marker and set its initial position
         marker = L.marker(firstPoint).addTo(map);

         const moveMarker = () => {
          if (progress < steps) {
           const newLat = firstPoint.lat + latStep * progress;
           const newLng = firstPoint.lng + lngStep * progress;
           const newLatLng = L.latLng(newLat, newLng);

           marker.setLatLng(newLatLng); // Update the marker's position

           progress++;
           setTimeout(moveMarker, intervalDuration);
          } else {
           // Marker reaches the second point, update money
           money +=
            Math.floor(Math.random() * (2000 - 1000 + 1)) +
            1000 * numberOfCarriages;
           const moneyDisplay =
            document.getElementById("moneydisplay");
           const moneyString = `£${money}`;
           moneyDisplay.textContent = moneyString;

           // Wait two seconds before animating back and call moveBackMarker recursively
           setTimeout(() => {
            moveBackMarker();
           }, 2000); // Wait for 2 seconds (2000 milliseconds)
          }
         };

         const moveBackMarker = () => {
          // Corrected calculation for animating back from second point to first
          if (progress > 0) {
           const newLat =
            secondPoint.lat - latStep * (steps - progress);
           const newLng =
            secondPoint.lng - lngStep * (steps - progress);
           const newLatLng = L.latLng(newLat, newLng);

           marker.setLatLng(newLatLng); // Update the marker's position

           progress--;
           setTimeout(moveBackMarker, intervalDuration);
          } else {
           console.log("Reached starting point again.");
           // Add random number to money and update display
           money +=
            Math.floor(Math.random() * (2000 - 1000 + 1)) +
            1000 * numberOfCarriages;
           const moneyDisplay =
            document.getElementById("moneydisplay");
           const moneyString = `£${money}`;
           moneyDisplay.textContent = moneyString;

           // Reset progress for next round trip
           progress = 0;

           // Recursively call moveMarker to start next animation cycle
           moveMarker();
          }
         };

         moveMarker(); // Start the animation
        });
       });
     }
    }
   });

   return circleMarker;
  },
 });
}

fetch("gb.geojson")
 .then((response) => response.json())
 .then((geojson) => {
  L.geoJSON(geojson, {
   fillColor: "none", // Style for polygon (empty fill)
   weight: 1,
   color: "#000",
   opacity: 1,
   fillOpacity: 0,
  }).addTo(map);
 })
 .catch((error) => {
  console.error("Error loading GeoJSON:", error);
 });

fetch("cities.geojson")
 .then((response) => response.json())
 .then((geojson) => {
  createCircleMarkers(geojson).addTo(map);
 })
 .catch((error) => {
  console.error("Error loading GeoJSON:", error);
 });
'