Water Is Pouring into a Conical Cistern at the Rate

Water is pouring into a conical cistern at the rate of 16 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) 0.10 ft/min.
B) 0.52 ft/min.
C) 0.18 ft/min.
D) 1.47 ft/min.