We know that in 1 km we have 1000 m and in 1 h we have 60 minutes and each minute have 60 seconds, then we multiply 60*60 to know how many seconds are in an hour and we have that 1 h have 3600 s. Using a conversion factor we have:
With this we can see that to convert a quantity from kn/h to m/s we must multiply by 1000 and divide by 36000