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

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 ?
4

Problem: two numbers are in the ratio of 7 : 6 . if 18 be subtracted from each , they are in the ratio of 6 : 5 . find the numbers ?
7,6

Problem: the ratio of the volumes of two cubes is 216 : 343 . what is the ratio of their total surface areas ?

31 : 36