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

Example 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 :
Example Output: d ) 21

Example Input: Problem: how many diagonals does a polygon with 13 sides have , if one of its vertices does not connect to any diagonal ?
Example Output: 54

Example Input: Problem: 10 women can complete a work in 5 days and 10 children take 10 days to complete the work . how many days will 5 women and 10 children take to complete the work ?
Example Output:
5