Calculate the speed of change in the distance between each pair of cars moving in the same direction

Calculate the speed of change in the distance between each pair of cars moving in the same direction, if the speeds of these cars are constant and equal, respectively, 80 km / h, 20 m / s, 1000 m / min.

Let’s translate the speed of cars in km / h:
First car: 80 km / h
Second car: 20 m / s = 20 * 60 * 60/1000 = 72 km / h
Third car: 1000 m / min = 1000 * 60/1000 = 60 km / h.
The difference between the speeds of cars 1 and 2: 80 – 72 = 8 km / h.
The difference between the speeds of cars 1 and 3: 80 – 60 = 20 km / h.
The difference between the speeds of cars 2 and 3: 72 – 60 = 12 km / h.