Task: Question Answering
Input (English): Problem: johnson completes a piece of work in 10 days , vincent completes the same work in 40 days . if both of them work together , then the number of days required to complete the work is 
Options: a ) 7 days , b ) 8 days , c ) 9 days , d ) 10 days , e ) 12 days
Output (English): b