6 hours. First, let's determine how far apart Leona and Sam are after 1 hour. At that time, the bus travelling East will be 60 miles away from the station, and the bus travel West will be 40 miles away from the station in the opposite direction. And since 60 + 40 = 100, Leona and Sam would be 100 miles apart from each other. So for every hour, their separation increases by 100 miles. Now all we need to do is divide 600 miles by 100 miles/hour to get the number of hours it would take to separate them by 600 miles. So: 600 miles / 100 miles/hour = 6 hours.
