Task: Question Answering
Input (English): Problem: every disk in a bag is either blue , yellow or green . the ratio of blue disks to yellow disks to green disks in this bag is 3 : 7 : 8 . if the total number of disks in the bag is 72 , how many more green disks than blue disks are in the bag ? 
Options: a ) 20 , b ) 28 , c ) 30 , d ) 35 , e ) 40
Output (English): a