Gravel Is Being Dumped from a Conveyor Belt at a Rate

Multiple Choice

Gravel is being dumped from a conveyor belt at a rate of 32 ft/min and its coarseness is such that it forms a pile in the shape of a cone whose base diameter and height are always equal. How fast is the height of the pile increasing when the pile is 10 ft high? Round the result to the nearest hundredth.

A) $0.41 ~\mathrm{ft} / \min$
B) $1.24 ~\mathrm{ft} / \min$
C) $0.14 ~\mathrm{ft} / \min$
D) $0.27 ~\mathrm{ft} / \min$
E) $0.6 ~\mathrm{ft} / \min$