The price is determined by the overall market. When you think of demand, you must wear the hat of a consumer or buyer. The definition of quantity demanded is the ability, willingness and desire to purchase a good or service. You must have all three in order to qualify. According to the Law of Demand , the answer is price.
Economists use a demand schedule to determine price and quantity demanded.
The schedule is simply a table made up of various prices and the amount of a product or service demanded at each individual price. Once you have figured that out, you plot the points on a graph, connect the dots and create a demand curve. Because the Law of Demand has an inverse relationship, the curve is downward-sloping. So, you can see in the example, as the price of movie tickets increases, the quantity demanded decreases and vice versa. When the price changes, we call that a movement along the curve.