Initially filled with water, a conical reservoir is 24 ft deep and 12 ft across the top. Water goose out from the bottom of the reservoir at the rate of 20 cu. ft per min. Find how fast the level of water is decreasing when the water is 10 ft deep, assuming that the orifice at the bottom have a negligible diameter.

Initially filled with water, a conical reservoir is 24 ft deep and 12 ft across the top. Water goose out from the bottom of the reservoir at the rate of 20 cu. ft per min. Find how fast the level of water is decreasing when the water is 10 ft deep, assuming that the orifice at the bottom have a negligible diameter.