Answer:
D. 75 km/h
Explanation:
Since the graph shows that the train is moving at a constant speed, it tells us that there is a slope.
For this one, you can just look at the graph since the time is already in hours.
When the time, in hours, is 1, the y is between 50 and 100. From 0 to 50, there is a unit in between and half of 50 is 25, so the spacing between each square in the y-axis is 25.
50+25=75
The train is moving at a speed of 75 km per hour.