Ignoring the fact that the axis are labeled incorrectly.
Evaluate each point using the velocity formula where d = distance, t = time, V = velocity
V = d/t
Now find the velocity at each point given.
So for the first point (omitting 0,0) we have:
V = 25,000/.25 = 100,000k/s
We have to switch the numbers up due to the fact that the axis are switch and for this to make sense we have to act like the time in seconds is the distance.
Now do this for every point and record them
1. 100,000
2. 66,667
3. 60,000
4. 66,667
5. 83,333
6. 100,000
7. 116,667
Now add all these numbers up and divide by the number of points
This gives you 84,762 k/s