Acar traveling 70 miles per hour is 20 miles behind a truck traveling 50 miles per hour. how long will it take the car to overtake the truck?

The truck in the lead is covering 50 miles in one hour.
The car behind is covering 70 miles in one hour.
The car is covering 20 miles more than the truck in one hour.
So the car gets 20 miles closer to the truck in one hour.

Since they were 20 miles apart at the beginning of the story,
one hour is enough time for the car to catch up to the truck.