The tank has two taps. Tap A is to fill the tank and tap B is to empty the tank. If only tap A can fill the tank in 35 hours, only tap B can empty the filled tank completely in 70 hours. Find how many hours it will take to fill the half empty tank completely.

The tank has two taps. Tap A is to fill the tank and tap B is to empty

1.	The tank has two taps. Tap A is to fill the tank and tap B is to empty the tank. If only tap A can fill the tank in 35 hours, only tap B can empty the filled tank completely in 70 hours. Find how many hours it will take to fill the half empty tank completely.
A.	40 hours
B.	70 hours
C.	35 hours
D.	55 hours
Answer» D. 55 hours