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 Q]: 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
[EX A]: d

[EX Q]: Problem: a is two years older than b who is twice as old as c . if the total of the ages of a , b and c be 12 , the how old is b ? 
Options: a ) 10 years , b ) 4 years , c ) 6 years , d ) 15 years , e ) 16 years
[EX A]: b

[EX Q]: Problem: b as a percentage of a is equal to a as a percentage of ( a + b ) . find b as a percentage of a . 
Options: a ) 62 % , b ) 73 % , c ) 41 % , d ) 71 % , e ) none of these
[EX A]:
a