there are two bikers biker one starts to travel at six miles

there are two bikers. biker one starts to travel at six miles per hour. three hours later biker two travels at ten miles per hour. how long does it take for biker two to catch up to biker one? Explain

3 hr lead=18 miles ahead
overtake at 10-6=4mph
18/4=4.5 hrs to catch up