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

Example Input: Problem: a student chose a number , multiplied it by 2 , then subtracted 138 from the result and got 102 . what was the number he chose ?
Example Output: 120

Example Input: Problem: if p / q = 3 / 11 , then 2 p + q = ?
Example Output: 17

Example Input: Problem: the present worth of rs . 2310 due years hence , the rate of interest being 15 % per annum , is :
Example Output:
rs . 1680