The entire race took Henry 1hr:36min which is 96min. He has an average speed of 30km/hr means he's been traveling 0.5km/min 30km/hr > 30km/1hr > 30km/60min = 0.5km/min since Henry took 96min to finish the race we multiply 0.5km/min with 96 0.5km/min*96min=48km
