I think there is a problem in the d/dt part

Problem:

A cone 4 m high, base diameter of 6 m, water is entering at 3 m^3 per minute

when water is at a height of 3 m, what is the rate of rise?

1/3pi(r^2)h = V

1/3pi(3^2)(3) = 28.274 m^3 at level of 3 m

dh/dt = ?

dv/dt= 2m^3/min

f'ghi + fg'hi + fgh'i + fghi' = dv/dt

0 + 0 + 1/3pi(2r)(dh/dt) + 1/3pi(r^2)(1)

working this out gets me a rate of

1.18 m^3/min

but I feel there is a problem in the fghi part