Jinkster,
A mate of mine did the PERF brush-up at Oxford, there is a similar question in there feedback and he shwed me how to work it out:
Two identical turbojets are at the same altitude and same speed and have the same specific fuel consumption. Plane 1 weighs 130000kg and has a fuel flow of 4300kg/hr. Plane 2 weighs 115000kg. what is the fuel flow?
a) 3804kg/hr
b) 4044kg/hr
c) 3364kg/hr <= correct answer
d) 3530kg/hr
(115000)2 / (130000)2 =0.7825 X 4300kg/hr = 3364kg/hr.
If you don't square the two weights you will get answer (a)
So with your question if you square the two weights you get answer (a),and if you don't you get answer (b).
Hope this will be of some help.
M