Task: Question Answering
Input (English): Problem: it takes avery 2 hours to build a brick wall while tom can do it in 4 hour . if the two start working together and after an hour avery leaves , how much time will it take tom to complete the wall on his own ? 
Options: a ) 70 , b ) 20 , c ) 50 , d ) 60 , e ) 30
Output (English): d