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.