A cistern which could be filled in 9 hours takes 1 hour more to be filled owing to a leak in its bottom.If the cistern is full, in what time will the leak empty it?	Choose the correct choice from the following
A) 50 hours	B) 62 hours	C) 90 hours	D) 75 hours	E) 100 hours

Rationale: "let the leak empty the full cistern in x hours 9 x / x - 9 = 9 + 1 x = 90 hours answer is c"
Answer: C