When gravel is deposited from a conveyor, it assumes the shape of an inverted right circular cone. The steepness of the pile depends on the average size and roughness of the pieces of gravel. For one particular grade of gravel, the ratio of the height of the cone to its radius is 3:2. The conveyor delivers 20 cubic feet per minute to the pile. How fast is the height of the pile increasing when its radius is 10 feet?