Hi there!
In order to find the average distance it flies in 1 hour, you first need to divide the time it takes to fly 2783km by the distance (2783km). This will give you the speed, which is also the average distance flown in 1 hour (it would be KILOMETERS PER HOUR).
5 3/4=5.75
2783/5.75=484
The plane averages 484km per hour.
Hope this helps!