An outlet pipe can empty a cistern in 3 hours. In what time will empty 2/3 of the cistern?

Answer: Option C

The outlet pipe empties the one complete cistern in 3 hours
Time taken to empty $$\frac{2}{3}$$ Part of the cistern
$$\begin{array}{rl}& \text{= }\frac{2}{3}\times 3\\ & =2\text{hours}\end{array}$$