It would take one hour because if you are traveling at 120 km/h, you cover a distance of 120 km for every hour that passes. Since the distance from Dubai to Fujairah is 120 km and you are figuring out how much time it'd take to get from one place to another, you'd have to divide the distance (120 km) by the speed (120 km/h), which should give you an answer of 1 hour.
