Hello, I am reviewing my psat and looking at the questions I got wrong. I can't understand how to do this problem.

Question

Mike and paul left their houses at the same time for a fitness run to the park. Mike ran at an average speed of 7 miles per hour. Paul ran at an average speed of 5 miles per hour. Mike and Paul arrived at the park at the same time. If Mike ran 4 miles farther than Paul, how far, in miles did Mike run?

Answer 1

Mike's time equals Paul's time.

Let D = Paul's distance in miles

Mikes time = (D+4miles)/(7mph)

Paul's time = D/5mph

(D+4miles)/(7mph) = D/(5mph)
Ssolve for D, then find D + 4.