Water Is Pouring into a Conical Cistern at the Rate

Multiple Choice

Water is pouring into a conical cistern at the rate of 18 cubic feet per minute. If the height of the cistern is 21 feet and the radius of its circular opening is 7 feet, how fast is the water level rising when the water is 16 feet deep? Round answer to nearest hundredth.

A) 0.12 ft/min.
B) 0.54 ft/min.
C) 0.20 ft/min.
D) 1.49 ft/min.