Task: Question Answering
Input (English): Problem: x can finish a work in 30 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 ) 3 , b ) 10 , c ) 6 , d ) 8 , e ) 9
Output (English): b