Task: Question Answering
Input (English): Problem: a can do a piece of work in 15 days . a does the work for 5 days only and leaves the job . b does the remaining work in 6 days . in how many days b alone can do the work ? 
Options: a ) 5 days , b ) 7 days , c ) 12 days , d ) 9 days , e ) 10 days
Output (English): d