An inverted cone of base radius 4cm and height 8cm is initially filled with water. Water drips out from the vertex at a constant rate of 2pi cm^3/s. Find the rate of decrease in the depth of the water in the cone 16seconds after dripping starts.

From what i understand:

dv/dt = -2pi cm^3/s

dh/dr = ?

Vol.of cone = (1/3)(pi)(r^2)(h)

dv/dh = 16pi/3

dv/dt = dh/dt * dv/dh

....

dh/dt = -2pi * (3/16pi) = -0.375cm/s

16seconds after dripping starts = 16 * -0.375

My ans was wrong, any idea what went wrong? Thanks in advance!