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: a man has some hens and cows . if the number of heads be 60 and the number of feet equals 200 , then the number of hens will be : 
Options: a ) 22 , b ) 25 , c ) 24 , d ) 20 , e ) 28

Ex Output:
d


Ex Input:
Problem: if 7 a - 3 b = 10 b + 50 = - 12 b - 2 a , what is the value of 9 a + 9 b ? 
Options: a ) - 9 , b ) - 6 , c ) 0 , d ) 6 , e ) 9

Ex Output:
c


Ex Input:
Problem: when x is even , [ x ] = x / 2 + 1 , when x is odd [ x ] = 2 x + 1 then [ 6 ] * [ 3 ] = ? 
Options: a ) [ 22 ] , b ) [ 44 ] , c ) [ 45 ] , d ) [ 28 ] , e ) [ 10 ]

Ex Output:

d