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 7 days , then the fraction of the work that is left is

Ex Output:
11 / 6


Ex Input:
Problem: the average of 6 no . ' s is 3.95 . the average of 2 of them is 3.8 , while the average of theother 2 is 3.85 . what is the average of the remaining 2 no ' s ?

Ex Output:
4.2


Ex Input:
Problem: if circles x and y have the same area and circle x has a circumference of 18 π , half of the radius of circle y is :

Ex Output:

4.5