A cistern is normally filled in 12 hrs,but takes 2 hrs longer to fill because of a leak on its bottom,if Cistern is full ,how much time citern would empty?  Choose the correct answer.
A) 10 hours B) 84 hours C) 30 hours D) 40 hours E) 50 hours

Rationale: "if leakage / hour = 1 / x , then 1 / 12 - 1 / x = 1 / 14 , solving 1 / x = 1 / 84 so in 84 hours full cistern will be empty . answer : b"
Answer: B