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

Example Input: Problem: if the average ( arithmetic mean ) of a and b is 45 and the average of b and c is 80 , what is the value of c − a ?
Example Output: 60

Example Input: Problem: the ratio of the radius of two circles is 1 : 3 , and then the ratio of their areas is ?
Example Output: 1 : 9

Example Input: Problem: a student chose a number , multiplied it by 2 , then subtracted 138 from the result and got 112 . what was the number he chose ?
Example Output:
125