Task: Question Answering
Input (English): Problem: x can finish a work in 18 days . y can finish the same work in 15 days . yworked for 10 days and left the job . how many days does x alone need to finish the remaining work ? 
Options: a ) 5 , b ) 4 , c ) 6 , d ) 7 , e ) 8
Output (English): c