Task: Question Answering
Input (English): Problem: a can do a job in 15 days and b in 20 days . if they work on it together for 3 days , then the fraction of the work that is left is ? 
Options: a ) 2 / 15 , b ) 8 / 15 , c ) 13 / 20 , d ) 1 / 12 , e ) 6 / 13
Output (English): c