Having that "n" there makes the problem look more scary. Don't worry about trying to use it in your equations. The "n" acts as a multiplication term when it is in front of the compund or whether it is a subscript of the compound. The "n" in the third equilibrium cancel each other out since they both multiply the compound the same amount, so ignore it and treat the problem the way you normally would.
This is an advanced way of looking at the problem and is not recommended. Maybe someone else can give you a better approach.