Task: Question Answering
Input (English): Problem: a can do a work in 15 days and b in 20 days . if they work on it together for 2 days , then the fraction of the work that is left is : 
Options: a ) 23 / 20 , b ) 5 , c ) 23 / 30 , d ) 23 / 12 , e ) 2
Output (English): c