Task: Question Answering
Input (English): Problem: a tank is filled by 3 pipes a, b, c in 3 hours. pipe c is twice as fast as b and b is twice as fast as a. how much will pipe a alone take to fill the tank ?
Options: a. 25 hr, b. 35 hr, c. 40 hr, d. 20 hr, e. 21 hr
Output (English): e