Task: Question Answering
Input (English): Problem: a can do a piece of work in 10 days and b alone can do it in 20 days . how much time will both take to finish the work ? 
Options: a ) a ) 5.333 , b ) b ) 6 , c ) c ) 6.666 , d ) d ) 8.333 , e ) e ) 9
Output (English): c