Task: Question Answering
Input (English): Problem: a tank is filled in 10 hours by 3 pipes a , b and c . pipe a is twice as fast as pipe b , and b is twice as fast as c . how much time will pipe b alone take to fill the tank ? 
Options: a ) 56 hours , b ) 28 hours , c ) 35 hours , d ) 66 hours , e ) 47 hours
Output (English): c