Drawing a picture may be helpful.
Try and write an expression to represent these actions.
Notice that Pierre and Dom must walk a combined total of 6 miles.
To find the amount of miles one person walks, you must multiply the rate by the time.
Let x represent the amount of time the two will have walked when they pass each other.
Since the two must walk a total of 6 miles:
At 1 hour, how many miles will Pierre have walked?
How far will he be from school?
2x + 4x = 6
x = 1 hour