A conical reservoir has a depth of 24 feet and a circular top of radius 12 feet. It is being filled so that the depth of water i increasing at a constant rate of 4 feet per hour. Determine the rate in cubic feet per hour at which water is entering the reservoir when the depth is 5 feet.

I know that A= 1/3(pi)hr^2 but i havent done rates for a while and I don't remember how to do this. Its calc ab