Task: Question Answering
Input (English): Problem: let f ( x , y ) be defined as the remainder when ( x – y ) ! is divided by x . if x = 24 , what is the maximum value of y for which f ( x , y ) = 0 ? 
Options: a ) 12 , b ) 15 , c ) 18 , d ) 20 , e ) 21
Output (English): d