calculus
posted by Jeffrey .
A spherical balloon is being inflated so that its volume is increasing at the rate of 200 cm3/min. At what rate is the radius increasing when the radius is 15 cm.

A car is heading east toward an intersection at the rate of 40 mph. A truck is heading south, away from the same intersection at the rate of 60 mph. At what rate is the distance between the car and the truck changing when the car is 8 miles from the intersection and the truck is 15 from the intersection?

V = (4/3) pi r^3
dV/dt = 4 pi r^2 dr/dt
200 = 4 pi (225) dr/dt