Gravel is being dumped from a conveyor belt at a rate of 20 ft/min. It forms a pile in the shape of a right circular

Gravel is being dumped from a conveyor belt at a rate of 20 ft³/min. It forms a pile in the shape of a right circular cone whose base diameter and height are always the same How fast is the height of the pile increasing when the pile is 21 ft high? The height is increasing at t/min