Pipe A can fill a tank in 10 hours. Due to a leak at the bottom, it takes 15 hours for the pipe A to fill the tank. In what time can the leak alone empty the full tank? Choose the correct answer:
A) 76
B) 84
C) 56
D) 75
E) 30

Rationale: let the leak can empty the full tank in x hours 1 / 10 - 1 / x = 1 / 15 = > 1 / x = 1 / 10 - 1 / 15 = ( 3 - 2 ) / 30 = 1 / 30 = > x = 30 . answer : e
Answer: E