Let the busses be A and B
The distance between A and B is 752 km
Let xkm/h represent the speed of bus A. If bus B travels 12 km/hour slower than bus B, it means that the speed of bus B is (x - 12)km/h
Recall,
Distance = speed * time
If they meet in 4 hours, it means that the total distance covered by each bus in 4 hours is 752km
Distance covered by A in 4 hours is x * 4 = 4x km
Distance covered by B in 4 hours is (x - 12) * 4 = (4x - 48) km
Therefore,
4x - 48 + 4x = 752
4x + 4x = 752 + 48
8x = 800
x = 800/8
x = 100
The rate of bus A is 100km/h
rate of bus B is 100 - 12 = 88km/h