Matt needs to travel 3 hours. If 40km=1 hour 400km=? But there are two distances 200/40*1=5 hours Therefore Kali needs to travel 5 hours to be 200 km away from the house. If 50km=1 hour 200km=? 200/50*1hr=4hrs Therefore Matt needs to travel 4hrs to be 200 km away from the house. But Kali traveled 1hr earlier than Matt. 4hrs-1hr=3hrs Therefore Matt has to travel for 3 hours to be 400km away from Kali.
