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

Example Input: Problem: a man , a woman and a boy can together complete a piece of work in 3 days . if a woman alone can do it in 6 days and a boy alone in 18 days , how long will a man take to complete the work ?
Example Output: 9 days

Example Input: Problem: if 1 / ( x + 4 ) + 1 / ( x - 4 ) = 1 / ( x - 4 ) , what is the value of x ?
Example Output: 4

Example Input: Problem: the total age of a and b is 12 years more than the total age of b and c . c is how many year younger than a
Example Output:
12