Explanation:

- To find the average speed, we must consider the total distance and total time taken for the journey.

- Let the total journey distance be 2D, with D being the distance for each half.

- The first half at 80 km/h takes time T1 = D/80.

- The second half at 100 km/h takes time T2 = D/100.

- Total time, T = T1 + T2 = D/80 + D/100.

- Simplifying, T = 180D/8000 = 9D/400.

- Average speed = Total distance (2D) / Total time (9D/400) = 800/9 km/h ˜ 88.89 km/h.

- Option 2: 88.89 km/h is the correct answer.