Two pipes A and B can fill a tank in 6 hours and 9 hours respectively. They are opened alternately for 1 hour each starting with pipe A first. In how many hours the tank will be filled?

Two pipes A and B can fill a tank in 6 hours and 9 hours respectively.

1.	Two pipes A and B can fill a tank in 6 hours and 9 hours respectively. They are opened alternately for 1 hour each starting with pipe A first. In how many hours the tank will be filled?
A.	5
B.	4
C.	6
D.	7
Answer» E.