Explanation:

- The girl from A to B completes the journey in 12 minutes at 5 km/h. Converting 12 minutes to hours, she travels for 12/60 = 0.2 hours. Therefore, the distance AB = 5 km/h x 0.2 hours = 1 km.

- The girl from B to A takes 25 minutes, which includes a 10-minute break. Thus, she travels for 15 minutes or 15/60 = 0.25 hours.

- To cover the same 1 km distance in 0.25 hours (actual traveling time), B's speed should be 1 km / 0.25 hours = 4 km/h.

- Option 3: 4 km/h is the correct speed for B.