Task: Question Answering
Input (English): Problem: a tank is filled by 3 pipes a , b , c in 6 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 ) 42 hr , c ) 40 hr , d ) 20 hr , e ) 50 hr
Output (English): b