Final answer:
The boat's effective speed going upstream is 5 km/h. In 3 hours, it will travel 15 km upstream against the river flow.
Step-by-step explanation:
The question involves calculating the distance travelled by a boat going upstream in a river. When a boat travels against the flow of a river, its effective speed is determined by subtracting the river's flow speed from the boat's speed in still water. Given that the river flows at 10 km/h and the boat travels upstream at 15 km/h relative to still water, the boat's effective speed upstream becomes 5 km/h (15 km/h - 10 km/h). To find out how far the boat will travel in 3 hours, we simply multiply the effective speed by the time: 5 km/h * 3 hours = 15 km. Thus, the boat will travel 15 kilometers upstream in 3 hours.