Question 933521
Let's say 'n' is the number of hours they take to be 225 miles apart.

The distance one bus travels in n hours is nX40 = 40n.
The distance second bus travels in n hours is nX50 = 50n.

So 40n + 50n = 225

=> 90n = 225
=> n = 225/90    >>> dividing by 90 on both sides

n = 2.5 hrs

It takes 2.5hrs for both the buses to be 225 miles apart.