The average speed is the distance divided by the time.
Total distance:
12.8 miles + 17.2 miles = 30 miles
Total time:
noon - 9:00 a.m. = 3 hours
6:00 p.m. - 1:00 p.m. = 5 hours
Total time = 3 hours + 5 hours = 8 hours
average speed = 30 miles / 8 hours = 3.75 miles per hour
