Natalie draw to the ferry office and back. the trip took five hours and the trip back took four hours. she average 80 km/h on the return trip. find the average speed of the trip there.

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

Yes you are correct

That they are numbers and related to each other.