what must be held constant in order to use Avogadros Law?

Please don't provide handwriting solution

What assumption is being made in determining each of the following?    The mass of the vapor. The volume of the vapor. The temperature of the vapor. The pressure of the vapor.

The human body burns glucose (C6H12O6) for energy according to this chemical reaction: C6H12O6+6O2→ 6CO2+6H2O The products of the reaction are carbon dioxide CO2 and water H2O Interestingly, all of the carbon dioxide and much of the water exits the body through the lungs: on every breath, the average person exhales 500.mL of air, which is typically enriched to 4% CO2 and 5% water vapor by volume. In short, when a person loses weight by dieting, the weight that is lost actually departs his body as a gas, every time he exhales. Each kilogram of body fat lost requires exhaling about 2.9kg of carbon dioxide. Calculate how many breaths it takes an average person to "exhale" 0.50kg  of fat. Round your answer to the nearest thousand. You'll need to know that the density of CO2 is 2.0 kg/m^3 .