Task: Question Answering
Input (English): Problem: x can finish a work in 21 days . y can finish the same work in 15 days . y worked for 5 days and left the job . how many days does x alone need to finish the remaining work ? 
Options: a ) 12 , b ) 13 , c ) 16 , d ) 14 , e ) 18
Output (English): d