Question 613968
1 hour = 55 km + 50 km = 105 km
2 hours = 105 km + 105 km(55km +50km)=210 km
3 hours = 210 km + 105 km = 315 km
4 hours = 315 km + 105 km = 420 km
it will be four hours til they are 420 km apart