It looks like there's a lot of extra information here. If the question only asks about the trip from Rohn to Nikolai, then the only information that matters is that the distance between the two is 121 km & that Seavey did it in 14 hours. Don't let the extra numbers throw you off.
As for the math behind this - km/hr is a math equation in and of itself. Any ratio like that is a simple division problem. Just plug your numbers (121 km / 14 hr) into the formula (km / hr) to get your answer!
EDIT: for future questions where they don't label it as clearly... velocity = the distance divided by the time.
