Task: Question Answering
Input (English): Problem: a , b , c can complete a piece of work in 21 , 6,12 days . working together , they complete the same work in how many days ? 
Options: a ) 2 , b ) 4 / 5 , c ) 7 / 9 , d ) 10 , e ) 84 / 25
Output (English): e