And within a capillary, oxygen and nitrogen can be exchanged with the environment. And we're using lungs because gases are exchanged within our lungs. So we want to find a number of blue molecules and a number of green molecules in terms of grounds found within one liter of this blood. So the first step is to realize that air is composed approximately 79% nitrogen and approximately 21% oxygen. Now, this translates to zero 79 mole fraction nitrogen and 0.2 1 mol fraction of oxygen. So the first step is to use rolled slow.