Question

Amy leaves a rest stop at 2 PM traveling west, at 45 miles per hour. Sarah leaves 2 hours later, also traveling west, but at 55 miles per hour. At what time will Amy catch up with Sarah?

Answer 1

they will catch up when they have the same mileage.

miles for amy: 45 * h + 45*2<- 2hours advantage
miles for Sarah: 55 * h

they will catch up when the mileage is equal

Answer 2

Per @mathessentials, solve the following for h:
45 * h + 45*2 = 55 * h