how to find the amount of time in hours

Question

A car leaves a town at 70 kilometers per hour. How long will it take a second car, travelling at 115 kilometers per hour, to catch the first car if it leaves 1 hour later?

Answer 1

Let h be the number of hours elapsed since the first car left

Equation for distance of first car: 70h

Equation for distance of second car: 115(h-1)

We want to set these two equal to each other (because that's when they've traveled the same distance, meaning the second car has caught up)

70h = 115(h-1)

70h = 115h - 115

45h = 115

h = 2.5555

it will take the second car just over 2.5 hours to catch up to the first car