The height of a rocket, launched from the ground, is given by the function y = 30t − 5t^2, where y is in meters and t is in seconds. An observer is sitting at ground level a distance d from the launch point. If r is the distance between the observer and where the rocket is, show that dr/dt = ((30t − 5t^2)(30 − 10t))/(sqrt((30t−5t^2)^2+d^2)). Show all your work.