Pipes A and B can fill a tank in 12 h and 18 h, respectively, whereas pipe C can empty the full tank in 8 h. A and B are opened for $$4\frac{1}{2}$$ hand then closed. C alone will empty the tank in (in h):

A

$$5\frac{1}{4}$$

B

$$9\frac{1}{2}$$

C

9

D

5