Two buses are moving towards each other, one at a speed of 40 mph and the other at a speed of 50 mph. How much closer to each other will they be in one hour? In two hours? In three hours?

They will be closer by ten hours in the first hour, but it'll get farther by ten as hours pass by, if you need a specific answer for this, you'll need a starting distance and an arrival place and specifically a time when the trains arrive in its destination. This problem lacks details.

What is the starting distance