Description for Correct answer:
Let C be the lime that Pipe C takes to empty the tank when Pipe A and Pipe B are closed.

Pipe A + Pipe B - Pipe C kept Open together results in a full tank getting emptied in 1 hour (60 min.)

\( \Large \frac{1}{12}+\frac{1}{15}-\frac{1}{C} = -\frac{1}{60} \) (negative sign indicates that the tank is getting emptied) or \( \Large \frac{1}{12}+\frac{1}{15}-\frac{1}{C}=\frac{1}{C}\ or\ C = 6\ minutes \)

If Pipe C can empty the tank in 6 minutes and it drains water at the rate of 22 liters/minute, then the capacity of the tank = \( \Large 6 \times 22 \) = 132 liters.