Pipe A can fill a tank in 2 hours. Due to a leak at the bottom, it takes 3 hours for the pipe A to fill the tank. In what time can the leak alone empty the full tank? Select the correct option:
A) 10 B) 9 C) 7 D) 6 E) 5

Rationale: "let the leak can empty the full tank in x hours 1 / 2 - 1 / x = 1 / 3 = > 1 / x = 1 / 2 - 1 / 3 = ( 3 - 2 ) / 6 = 1 / 6 = > x = 6 . answer : d"
Answer: D