Explanation:

Given:
- Two cars start from points A and B on a highway, which are 80 km apart.
- The cars travel in the same direction.
- The cars meet after 4 hours.

To understand this scenario, let's break down the problem and analyze it step by step.

Step 1: Identifying the variables:
- Distance between points A and B: 80 km
- Time taken to meet: 4 hours

Step 2: Understanding the scenario:
- Since the cars travel in the same direction, their speeds can be compared to determine their relative speed.
- Let's assume the speed of the car starting from point A is S1 km/h and the speed of the car starting from point B is S2 km/h.

Step 3: Calculating the relative speed:
- The relative speed of the two cars can be calculated by subtracting the slower speed from the faster speed.
- Relative speed = |S1 - S2| km/h

Step 4: Calculating the distance traveled by the slower car:
- The slower car will take 4 hours to meet the faster car.
- Distance traveled by the slower car = S2 * 4 km

Step 5: Calculating the distance between the two cars when they meet:
- When the cars meet, the distance traveled by the slower car plus the distance between the two cars should be equal to the total distance between points A and B.
- Distance traveled by the slower car + Distance between the two cars = 80 km
- S2 * 4 + Distance between the two cars = 80 km

Step 6: Solving the equation:
- Rearranging the equation from step 5, we can find the distance between the two cars when they meet.
- Distance between the two cars = 80 km - S2 * 4 km

Step 7: Calculating the relative speed:
- Since the cars meet after 4 hours, we can calculate the relative speed using the distance between the two cars when they meet.
- Relative speed = (80 km - S2 * 4 km) / 4 h

Step 8: Solving the equation:
- The relative speed can also be calculated by subtracting the slower speed from the faster speed.
- Relative speed = |S1 - S2| km/h

Step 9: Equating the two expressions for relative speed:
- We can equate the two expressions for relative speed to solve for the speeds of the two cars.
- |S1 - S2| km/h = (80 km - S2 * 4 km) / 4 h

Step 10: Solving the equation:
- Solving the equation from step 9 will give us the speeds of the two cars.

Step 11: Conclusion:
- By following the above steps, we can determine the speeds of the two cars and understand how they meet after 4 hours on the highway.