Two pipes A and B can fill a tank in 36 min. and 45 min. respectively. Another pipe C can empty the tank in 30 min. First A and B are opened. After 7 minutes, C is also opened. The tank filled up in:

Two pipes A and B can fill a tank in 36 min. and 45 min. respectively.

1.	Two pipes A and B can fill a tank in 36 min. and 45 min. respectively. Another pipe C can empty the tank in 30 min. First A and B are opened. After 7 minutes, C is also opened. The tank filled up in:
A.	9 min.
B.	6 min
C.	0 min.
D.	5 min.
Answer» B. 6 min