Well I found that HCl was the limiting reagent. I figured that since the equation is a 1:1 ratio I could just set the mols of NH4Cl as the mols of HCl and solve for the pressure using the ideal gas law. Apparently there is another step, where I have to subract the mols of the two gasses, and then use THAT value in the gas law. What is going on here? How is that value the number of mols in the NH4Cl?