Task: Question Answering
Input (English): Problem: a can do a piece of work in 4 hours ; b and c together can do it in 2 hours , which a and c together can do it in 2 hours . how long will b alone take to do it ? 
Options: a ) 2 hours , b ) 3 hours , c ) 4 hours , d ) 5 hours , e ) 6 hours
Output (English): c