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: arjun started a business with rs . 20,000 and is joined afterwards by anoop with rs . 80 , 000 . after how many months did anoop join if the profits at the end of the year are divided equally ?

Ex Output:
9

Ex Input:
Problem: if n = ( 33 ) ^ 43 + ( 53 ) ^ 33 what is the units digit of n ?

Ex Output:
4