Description for Correct answer:
Pipe A fills at the rate of 35 gallons per 10 minutes = 3.5 gallons per minute.

Pipe A is kept open for 12 minutes. So, the water discharged in as min. = \( \Large 12 \times 3.5 = 42 gallons \)

When pipe A was opened the tank was 2/3rd empty.

Therefore, 42 gallons = 2/3rd the total capacity of the tank.

Hence, the capacity of the tank = \( \Large \frac{3}{2} \times 42 = 63 gallons \)