Task: Question Answering
Input (English): Problem: a and b can do a piece of work in 10 days and 10 days respectively . they work together for 10 days and b leaves . in how many days the whole work is completed ? 
Options: a ) 30 days , b ) 40 days , c ) 50 days , d ) 60 days , e ) 70 days
Output (English): a