Distance covered by them in the 1st hour = 17.5 km Distance covered by them in the 2nd hour = 16.5 km Distance covered by them in the 3rd hour = 15.5 km Distance covered by them in the 4th hour = 14.5 km Distance covered by them in the 5th hour = 13.5 km Distance covered by them in the 6th hour = 12.5 km = 90 km Hence, they will meet after 6 hours.