How many hours would it take Pump \(A\) and Pump \(B\) working together, each at its own constant rate, to empty a tank that was initially full?
(1) Working alone at its constant rate, Pump \(A\) would empty the full tank in \(4\) hours \(20\) minutes.
(2) Working alone, Pump \(B\) would empty the full tank at its constant rate of \(72\) liters per minute.
Answer: E
Source: Official Guide