Grain is ejected from a chute at the rate of 0.1 m3/min and is forming a heap on a flat horizontal floor. The heap is in the form of a circular cone of semi-vertical angle 45 degrees. Find the rate, in metres per minute, at which the height of the cone is increasing, at the instant 3 minutes after the opening of the chute.

Setting out:

dV/dt = 0.1 m3/min

dh/dt

= dV/dt * dh/dV

= 0.1 * dh/dV

V = 1/3 pi r^2 h

= 1/3 pi h^3

dV/dh = pi h^2

dh/dV = 1/(pi h^2)

dh/dt = 1/(10 pi h^2)

BUT I am trying to substitute a value of t...HELP! where did i go wrong???