Task: Question Answering
Input (English): Problem: a can do a piece of work in 7 days and b can do it in 6 days how long will they both work together to complete the work ? 
Options: a ) 6 / 11 , b ) 8 / 13 , c ) 3 / 13 , d ) 9 / 11 , e ) 10 / 13
Output (English): c