A right conical tank with the point oriented down, a height of 19 feet, and a radius of 5 feet has sprung a leak. How fast is the volume of water in the tank changing when the water is 13 feet high, and the water level changes at a rate of 18 inches per minute?
a) 21π ft³/min
b) 28π ft³ /min
c) 35π ft³ /min
d) 42π ft³ /min
