A cistern is normally filled in 10 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? Pick:
A) 33 B) 88 C) 60 D) 99 E) 11

Rationale: "1 / 10 - 1 / x = 1 / 12 x = 60 answer : c"
Answer: C