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'.

Input: Consider Input: Problem: if ( a - b - c + d = 13 ) and ( a + b - c - d = 9 ) , what is the value of ( b - d ) ^ 2 ? 
Options: a ) 4 . , b ) 8 . , c ) 12 . , d ) 16 . , e ) 64 .

Output: a


Input: Consider Input: Problem: what is the average of first 21 multiples of 5 ? 
Options: a ) a ) 70 , b ) b ) 77 , c ) c ) 55 , d ) d ) 81 , e ) e ) 82

Output: c


Input: Consider Input: Problem: if n divided by 9 has a remainder of 8 , what is the remainder when 2 times n is divided by 9 ? 
Options: a ) 1 , b ) 7 , c ) 3 , d ) 5 , e ) 6


Output: b