Two buses leave houston at the same time and travel in opposite directions. one bus averages 55 miles per hour, and the other bus averages 45 miles per hour. when will they be 400 miles apart

Well there can be two different solutions for this but i will choose the easier one. Obviously one requires a system of equations which obviously will involve a lot of thinking and some good algebra solving in order for them to solve.

As for hit and trial it is very easy, we can just keep adding the distance as we know they are in different directions. 55 + 45 = 100. So 100 x 4 = 400 miles. So after around 4 hours they will be 400 miles apart if they continue at the same pace.