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

Example Input: Problem: two tains of equal lengths take 10 seconds and 15 seconds respectively to cross a telegraph post . if the length of each train be 120 metres , in what time ( in seconds ) will they cross each other travelling in opposite direction ?
Example Output: 12

Example Input: Problem: a solution of 70 litres contains oil and water in the ratio 9 : x . if 6 litres of water is added to the solution , the ratio becomes 6 : 4 , find the value of x ?
Example Output: 

Example Input: Problem: a class of boys stands in a single line , one boy is 19 th in order from both the ends , how many boys are there in the class ?
Example Output:
37