A truck enters a highway - college algebra

Question

A truck enters a highway driving 60 mph. A car enters the highway at the same place 15 minutes later and drives 72 mph in the same direction. From the time the car enters the​ highway, how long will it take the car to pass the​ truck?

Answer 1

In 15 mins, i.e, (1 / 4) hours, the truck is already (60 mph) * ((1 / 4) h) = 15 miles ahead of the car.

The car gains (72 mph - 60 mph) * (1 h) = 12 miles on the truck every hour.

So the car reaches the truck in (15 / 12) = ___ hours.