The task is to generate the correct answer for a given math problem.

Ex Input:
Problem: a father said to his son , ' ' i was as old as you are at the present at the time of your birth ' ' . if the father ' s age is 52 years now , the son ' s age 5 years back was :

Ex Output:
d ) 21

Ex Input:
Problem: the average of 10 numbers is 0 . in those 10 , at the least , how many may be greater than or equal to zero ?

Ex Output:
1

Ex Input:
Problem: the h . c . f . of two numbers is 30 and the other two factors of their l . c . m . are 15 and 12 . the larger of the two numbers is

Ex Output:
450