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: how many positive integers less than 100 have a remainder of 6 when divided by 13 ? 
Options: a ) 2 , b ) 7 , c ) 6 , d ) 9 , e ) 10

Ex Output:
c


Ex Input:
Problem: a cyclist rides a bicycle 8 km at an average speed of 10 km / hr and again travels 10 km at an average speed of 8 km / hr . what is the average speed for the entire trip ? 
Options: a ) 9.28 , b ) 8.48 , c ) 8.78 , d ) 8.98 , e ) 9.18

Ex Output:
c


Ex Input:
Problem: if a ^ 2 + b ^ 2 = 177 and ab = 54 then find the value of a + b / a - b ? 
Options: a ) 1 , b ) 3 , c ) 5 , d ) 7 , e ) 9

Ex Output:

c