Two buses leave houston at the same time and travel in opposite directions. one bus averages 55 mi/h and the other bus averages 45mi/h. when will they be 400 mi apart?

4 hours after they leave Houston. Easiest way to solve this problem is to first calculate the relative velocities of the two buses. Since they're traveling in opposite directions, you simply need to add their respective velocities to see what the relative velocity is between them. 55 mi/h + 45 mi/h = 100 mi/h That means that the buses will increase their distance apart from each other by 100 miles for every hour that they travel. So divide 400 miles by 100 miles/hour 400 miles / 100 miles/hour = 4 hours. So 4 hours after the buses start moving, they will be 400 miles apart from each other.