how do you do this rate of change question?

Question

The dimensions of a conical tank is of radius 3 m and height 6 m. Water is added to it at a

rate of π m³/min. Find the rate of change of the water level when the height is 3 m.

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

Answer 1

V = (pi/3)r^2h

r=h/2

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

= (pi/3)h^3/2 ^2

= (pi/12)h^3

V' = (pi/4)(h^2)h'

h=3

V'(3) = (9pi/4)(h') = pi

(9/4)h' = 1

h' = 4/9 meters per minute

rate of change in height = 4/9 m/min when h=3

h' = about 0.44 m/min