To obtain the largest and smallest function values, evaluate f at its critical numbers and at the endpoints of the interval. This enables us to draw a rough sketch like the one below. Then use the numerical data to resolve the constant. Substitute the numerical data into this equation and solve for the decay constant k. Then use this to define the amount of radon as a function of time.
Maple agrees with our findings.
Here are the steps involved in the implicit differentiation. While Maple can do this via brute force, we would draw a right triangle and use trigonometry. Draw a simple sketch of a rectangular box, labeling it as follows. You did have to derive something for this problem to get full credit. General formula for position under constant acceleration.