Explanation:

- The downstream speed is calculated by dividing the distance by the time: 120 km / 3 hours = 40 km/h.

- The upstream speed is calculated similarly: 120 km / 6 hours = 20 km/h.

- The speed of the boat in still water is the average of the downstream and upstream speeds: (40 km/h + 20 km/h) / 2 = 30 km/h.

- In still water, the boat covers 30 km in one hour.

- To find the distance covered in 4 hours in still water, multiply the speed by the time: 30 km/h * 4 hours = 120 km.

- Thus, in 4 hours, the boat will cover 120 km in still water.

Your answer is RIGHT