Answer:
So the Conclusion is that 4000 km/h is the constant speed.
Explanation:
Given:
Time (hrs) | Distance (km)
0.5 | 2000
 1 | 4000 
 1.5 | 6000
 
To Find:
 Constant Speed:
Solution:
We know ,
 
 
For the first case we have

For the second case we have

For the third case we have

So the Conclusion is that 4000 km/h is the constant speed