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

Example Input: Problem: a is twice as good a workman as b and they took 6 days together to do the work b alone can do it in .
Example Output: 18 days

Example Input: Problem: two cars start at the same time from opposite ends of a highway that is 175 miles long . one car is riding at 25 mph and the second car is riding at 45 mph . how long after they begin will they meet ?
Example Output: 2.5

Example Input: Problem: a cistern is filled by pipe a in 12 hours and the full cistern can be leaked out by an exhaust pipe b in 18 hours . if both the pipes are opened , in what time the cistern is full ?
Example Output:
36 hrs