Explanation:

- The man completes the journey in 10 hours total.

- The journey is split into two halves.

- For the first half, the man's speed is 21 km/h.

- For the second half, the man's speed is 24 km/h.

- Let's denote the distance of each half of the journey as "d".

- Time taken for the first half = d / 21 hours.

- Time taken for the second half = d / 24 hours.

- Total time = (d / 21) + (d / 24) = 10 hours.

- Solving the equation: (8d / 168) + (7d / 168) = 10

- 15d / 168 = 10

- 15d = 1680

- d = 112

- Total distance = 2d = 224 km.

Option 2: 224 km is the correct answer.