Math constant speed, average speed

Question

Cars A and B leave the same place and travel in the same direction along a straight road. Car A travels at 60 km/h and car B travels at 72 km/h. After how long will they be at 8km apart?

Answer 1

The difference in their distance is 12km/h (72-60).

12/(1 hour) = 8/(x hours) so 12 = 8/x

Multiply both sides by x:

12x = 8

Divide both sides by 12:

x = 8/12 = 2/3 hours

2/3(hours) x 60(min/hour) = 120/3 = 40 minutes