Draw? Didn't Natalie DRIVE to the office and then back?
Average speed = total distance divided by total time.
Total distance = speed times time = 80 km/hr times 4 hours, or 320 km.
Then, back to the main question:
Total distance = 2(320 km)
Total time elapsed = 9 hrs
640 km
Average speed = ------------- = 71.1 km/hr
9 hrs