I'm having a tough time answering this question, and help would be greatly appreciated.

A reservoir is shaped like an inverted cone. Its height is 6m and the diameter of its top face is 4m. It empties its water with a faucet located at its lower end (the apex of the cone). We would like to determine the rate at which the water empties from the cone at the moment when the water level in the cone is at 4m, given that, at the same moment the level lowers at a rate of 3cm/s.

To solve this problem, let x be the water level in the reservoir (in m), V the volume of water it contains (in m^3), and the time (in s).

a) Express V as a function of x.

b) Compute dV/dt at the moment in question. Give the answer with three decimals precision, paying attention to the sign.