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

Ex Input:
Problem: excluding stoppages , the speed of the bus is 54 kmph and including stoppages , it is 36 kmph . for how many minutes does the bus stop per hr

Ex Output:
20 mi

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

Ex Output:
1 : 9

Ex Input:
Problem: if a person walks at 20 km / hr instead of 10 km / hr , he would have walked 40 km more . the actual distance traveled by him is ?

Ex Output:
40 km