26375
On the graph, it tells you how much fuel is left after 2 hours of the journey.
If we take 422,000 and subtract 369,250 from it we get 52,750. However, this is how much gas is used in 2 hours, so to find one hour we need to divide by 2, getting us 26,375.
Therefore, the Jet uses 26,375 gallons per hour during the 16 hour trip from Los Angeles, CA to Melbourne, Australia.