Working at constant rate, pump X pumped out half of the water in a flooded basement in 3 hours. The pump Y was started and the two pumps, working independently at their respective constant rates, pumped out rest of the water in 3 hours. How many hours would it have taken pump Y , operating alone at its own constant rate, to pump out all of the water that was pumped out of the basement? Choose the correct choice from the following choices:
A) a . 20	B) b . 12	C) c . 14	D) d . 18	E) e . 24

Rationale: "rate of x = 1 / 8 rate of x + y = 1 / 6 rate of y = 1 / 6 - 1 / 8 = 1 / 24 20 hours a"
Answer: A