The first step is to always identify and write down the given variables mathematically.
For question 14, you can draw a right-triangle with Inge at the ground vertex, and the kite at the top vertex. The string is the hypotenuse, so the height of the kite above the ground is the vertical leg which is 300ft. The length of the horizontal leg is variable with time, we'll call it x. We are given dx/dt = 25 ft/s. We want to find ds/dt when x=500ft, where s is the length of the string. We note that ds/dt = (ds/dx)(dx/dt) by the chain rule. Thus, if we write a function s = s(x) and differentiate it at x = 500ft, we will have the missing rate in our equation. Can you find an equation relating s and x ?
