Task: Question Answering
Input (English): Problem: a can do a job in 30 days and b in 40 days . if they work on it together for 10 days , then the fraction of the work that is left is ? 
Options: a ) 2 / 11 , b ) 3 / 13 , c ) 5 / 12 , d ) 7 / 10 , e ) 6 / 15
Output (English): c