B. 8 min
Feedback Tank can be filled by pipe A in 12 minutes and pipe B in 24minutes.
=> Part filled by A in 1 minute= 1/12
=> Part filled by B in 1 minute= 1/24
=> Part filled by both in 1 minute= 1/12 + 1/24
= 3/24=1/8
Time taken to fill the entire tank = 8 minutes