A cistern is normally filled in 12 hours but takes two hours longer to fill because of a leak in its bottom. If the cistern is full, the leak will empty it in? Choose the correct choice from the following options:
A) 33
B) 84
C) 40
D) 99
E) 11

Rationale: "1 / 12 - 1 / x = 1 / 14 x = 84 answer : b"
Answer: B