Answer:
It is 5 km/hour
Step-by-step explanation:
Let w represents the speed of the water
The speed can be found by following:
→ distance = speed x time → speed = distance / time (1)
If the boat goes downstream the total speed of the boat is the speed of the boat in still water + the speed of the water. Substitute the values into equation 1:
→ (the speed of the boat in still water + the speed of the water) = 120 / 4
Since the speed of the boat in still water is 25
→ 25 + w = 120 / 4
→ w + 25 = 30
→ w = 5
