[rj1027]

the question I have has been bugging because i feel that I do not have enough info.  

the question is :

If the average person wieghs 65 kg and generates 10 Mj of eneryg/day as heat then:

If the individual did not eat anything how much fat would be used in a day to generate that energy? (use Hess's Law)

Now if someone could just explain how i apply Hess's law to this question that would be great.

[Demotivator]

Well now, Fat respiration:
Fat(s) + nO2 (g)-> xCO2(g) + yH2O(l) + energy

Knowing the standard molar enthalpies of formation of CO2(g) and H2O(l) and fat (s) , the energy released can be calculated per  above mass lost. Total mass lost can be calculated given your value of total energy per day.
It's assumed that you can get the molar enthalpies of formation of  
CO2(g)  and H2O(l)  from some source. But you'd also need the enthalpy and formula for the fat and to balance the equation. I do not know if that info is somewhere in your study material or not.