Task: Question Answering
Input (English): Problem: a can do a work in 40 days , b in 60 days . a alone start the work after 10 days he left work . in how many days b can finish the work ? 
Options: a ) 20 days , b ) 15 days , c ) 30 days , d ) 45 days , e ) 50 days
Output (English): d