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

Ex Input:
Problem: if a drawing has an outer circle of diameter 30 and an inner circle of diameter 24 , then what fraction of outer circle ' s surface is not covered by the inner circle ?

Ex Output:
9 / 25', 'e ) 2 / 3'


Ex Input:
Problem: excluding stoppages , the average speed of a bus is 60 km / hr and including stoppages , the average speed of the bus is 15 km / hr . for how many minutes does the bus stop per hour ?

Ex Output:
4


Ex Input:
Problem: a train passes a platform in 34 seconds . the same train passes a man standing on the platform in 20 seconds . if the speed of the train is 54 km / hr , the length of the platform is

Ex Output:

210 meter