Hi there,

So, we have the distance he covered during the first 4 hours, find the distance that has to be covered, which you can calculate in meters 42000 - (4*6000) = 42 000 - 24 000 = 18000m

The speed would be more confortable to be calculated as m/min, which gives you 6km/hr = 6000m/60min = 100m

He is left with 2hr42 min, or 162min - get now the speed with which he needs to cover those 18000m;

The percentage you can evaluate in the end, hope this helps,