Two taps A, B can fill a cistern in 8, 12 hours respectively. Both are opened at the same instant and after $$x$$ hours tap B is stopped and tap A continued. If the total time taken to fill the cistern is 5 hours, then $$x$$ =

A

3

B

$$3\frac{1}{2}$$

C

4

D

$$4\frac{1}{2}$$