Breguet's range equation can be used to determine the fraction of fuel burnt under this mission segment:
The lift to drag ratio 
is found using 
method and by knowing that
lift equals weight, but that would require that we already knew the
weight, which we do not at this time. Instead we could go back to
our statistical data and find out what 
could be, and make the estimation
that cruise will occur at .866 of that figure (jet aircraft).