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

Example Input: Problem: a bag contains 12 red marbles . if someone were to remove 2 marbles from the bag , one at a time , and replace the first marble after it was removed , the probability that neither marble would be red is 25 / 36 . how many marbles are in the bag ?
Example Output: 48

Example Input: Problem: by selling an article for $ 225 a person gains $ 75 . what is the gain % ?
Example Output: 50 %

Example Input: Problem: how many seconds will a 1000 meter long train take to cross a man walking with a speed of 3 km / hr in the direction of the moving train if the speed of the train is 63 km / hr ?
Example Output:
300