Task: Question Answering
Input (English): Problem: a , b and c can do a piece of work in 24 days , 30 days and 60 days respectively . they began the work together but c left 4 days before the completion of the work . in how many days was the work completed ? 
Options: a ) 10 days , b ) 11 days , c ) 13 days , d ) 21 days , e ) 31 days
Output (English): b