Tap A can fill an empty tank in one hour, while a drain pipe B can empty that full tank in 6 hours. If both A and B are opened at the same instant, the total time taken to fill that empty tank,in hours, is

A

$$\frac{5}{6}$$

B

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

C

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

D

$$\frac{6}{5}$$