Task: Question Answering
Input (English): Problem: a can complete a project in 20 days and b can complete the same project in 40 days . if a and b start working on the project together and a quits 10 days before the project is completed , in how many days will the project be completed ? 
Options: a ) 18 days , b ) 20 days , c ) 26.67 days , d ) 16 days , e ) 12 days
Output (English): b