Two pipes A and B can fill an empty cistern in 4.8 and 7.2 hours, respectively. Pipe C can drain the entire cistern in 9.6 hours when no other pipe is in operation. Initially when the cistern was empty, Pipe A and Pipe C were turned on. After a few hours, Pipe A was turned off and Pipe B was turned on instantly. In all it took 16.8 hours to fill the cistern. For how many hours was Pipe B turned on?

Two pipes A and B can fill an empty cistern in 4.8 and 7.2 hours, resp

1.	Two pipes A and B can fill an empty cistern in 4.8 and 7.2 hours, respectively. Pipe C can drain the entire cistern in 9.6 hours when no other pipe is in operation. Initially when the cistern was empty, Pipe A and Pipe C were turned on. After a few hours, Pipe A was turned off and Pipe B was turned on instantly. In all it took 16.8 hours to fill the cistern. For how many hours was Pipe B turned on?
A.	11.55
B.	12.6
C.	10.5
D.	10.8
Answer» E.