In this task, you need to answer the given multiple-choice question on the general math. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Example Input: Problem: if ( a – b ) is 9 more than ( c + d ) and ( a + b ) is 3 less than ( c – d ) , then ( a – c ) is : 
Options: a ) 6 , b ) 2 , c ) 3 , d ) 4 , e ) 5
Example Output: c

Example Input: Problem: in a group of ducks and cows , the total number of legs are 36 more than twice the number of heads . find the total number of cows . 
Options: a ) 12 , b ) 14 , c ) 16 , d ) 18 , e ) 20
Example Output: d

Example Input: Problem: the average of 5 numbers is 27 . if one number is excluded the average become 25 . the excluded number is : 
Options: a ) 25 , b ) 27 , c ) 30 , d ) 35 , e ) 37
Example Output:
d