>>11483461This is correct, 4km/h
Up: 6000m/5400s = 1.1111...m/s
Down: 6000m/2700s = 2.2222...m/s
Difference is 1.1111...m/s which is the velocity without the paddling and that is roughly 4km/h
But i think you missunderstood me about the paddling part.
If you stop paddling you would go down the river with a constant speed, that is the speed of the current. Now if you start paddling you either increase the total velocity if you go with the current, or you decrease it if you go against it.
The paddle velocity vp has to be the same in both directions, otherwise you can not calculate this with the given information.
