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

Example Input: Problem: 30 pens and 75 pencils were purchased for 750 . if the average price of a pencil was 2.00 , find the average price of a pen .
Example Output: 20

Example Input: Problem: two trains each 120 m in length each , are running on two parallel lines in opposite directions . if one goes at the speed of 85 km / h while the other travels at 65 km / h . how long will it take for them to pass each other completely .
Example Output: 10.07 sec

Example Input: Problem: the average weight of 4 students decreases by 8 kg when one of them weighing 96 kg is replaced by a new student . the weight of the student is
Example Output:
64 kg