A tank has two taps A and B. The taps A and B can empty a full tank in 6 hours and 8 hours respectively. Both are opened at same instant and after 2 hours. B is closed. Total time taken to fill the empty tank (in hours) is

A

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

B

3

C

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

D

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