The formula for the volume of a cone is V=1/3 πr^2h, where r is radius and h is height

The formula for the volume of a cone is V = 1/3 πr2h, where r is radius and h is height. Find the rate of change of the volume for each of the radii given below if dr/dt is 9 inches per minute and h = 24r.

(a) r = 5 inches
(b) r = 21 inches