For if you start at 1 hour you end up with one bus 45 miles away from the school and the other 40 miles. If you then add these then you find out how far apart they are which is 85 at this point and time. If you do another hour the bus going 45 is now 90 miles away from the school. The other one will be 80. After you add these two number to find how far apart they are you end up with 170.
