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'.

Ex 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 .

Ex Output:
a


Ex Input:
Problem: the average age of 15 students of a class is 15 years . out of these , the average age of 8 students is 14 years and that of the other 6 students is 16 years , the age of the 15 th student is 
Options: a ) 17 , b ) 12 , c ) 13 , d ) 14 , e ) 15

Ex Output:
a


Ex Input:
Problem: simplify : 256 x 256 - 144 x 144 
Options: a ) 761200 , b ) 44800 , c ) 761800 , d ) 761500 , e ) none of them

Ex Output:

b