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

Example Input: Problem: find the sum the difference between the compound and s . i . on a certain sum of money for 5 years at 20 % per annum is rs . 75 of money ?
Example Output: 1875

Example Input: Problem: a can do a work in 15 days and b in 20 days . if they work on it together for 7 days , then the fraction of the work that is left is
Example Output: 11 / 6

Example Input: Problem: if 2 + 3 = 13 ; 3 + 5 = 31 ; 5 + 7 = 59 , then 7 + 9 = ?
Example Output:
95