Explanation:

- To find the speed of the train, we need to calculate how fast it passes each person.

- Both people and the train are moving in the same direction.

- Using relative speed, subtract each person's speed from the train's speed.

- The first person travels at 4 km/h, and the train takes 12 seconds to pass.

- The second person travels at 6 km/h, and the train takes 14 seconds to pass.

- Convert 12 and 14 seconds to hours for calculation, as speed is in km/h.

- Calculate the relative speed in each case and use it to solve for the train's speed.

- Option 1: 18 km/h: This option is incorrect because it doesn't fit the calculations.

- Option 2: 26 km/h: This option doesn't match either scenario.

- Option 3: 20 km/h: This is incorrect.

- Option 4: 24 km/h: Correct. The train is moving fast enough to cover the differences consistently.