Flight range question

Hi,
I was reading about the technical features of the Boeing 757 airliner and I saw that the maximum flight range was of 3,900 nautical miles, as described by Boeing in this link: http://www.boeing.com/commercial/757...f_200tech.html.
Out of curiosity, I was wondering how this figure can be calculated, so I tried using the graph shown at page 35 of this document: http://www.boeing.com/commercial/air...aps/757_23.pdf, but I'm not sure about how to actually do it. For example, how could you calculate the flight range in nautical miles for an airplane without passengers and using the maximum amount of fuel? I figured this would be the actual maximum range for this aircraft model.
Thanks for your help.