Task: Question Answering
Input (English): Problem: a and b can do a work in 12 days , b and c in 30 days and c and a in 36 days . in how many days will the work be completed , if all three of them work together ? 
Options: a ) 180 / 15 , b ) 180 / 10 , c ) 180 / 13 , d ) 180 / 15 , e ) 180 / 11
Output (English): c