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

Ex Input:
Problem: a can do a work in 15 days and b in 20 days . if they work on it together for 5 days , then the fraction of the work that is left is

Ex Output:
5 / 12


Ex 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 ?

Ex Output:
60


Ex Input:
Problem: a train 124 m long running at 68 kmph crosses a platform in 19 sec . what is the length of the platform ?

Ex Output:

234