Ok I have done this problem several times over and my computer is telling me that all of my answers are wrong . Please help!

We assume that an oil spill is being cleaned up by deploying bacteria that consume the oil at

cubic feet per hour. The oil spill itself is modeled in the form of a very thin cylinder as depicted below. Its height

is the thickness of the oil slick. Suppose at some moment in time the height is decreasing at

foot per hour, the thickness of the slick is

foot, and the cylinder is

feet in diameter. At what rate is the area covered by the slick changing at that moment? (That is, the area of the base disc of the cylinder).

I have been finding dr/dt by taking the derivative wrt time of v+pir^2*h and then using dr/dt to find dA/dt by deriving A=pi*r^2. Please Help!