50.0g of N2O4 is introduced into an evacuated 2.00L vessel and allowed to come to equilibrium with its decomposition product, N2O4 (g)---? 2NO2(g). For this reaction Kc=0.133. Once the system has reached equilibrium, 5.00g of NO2 is injected into the vessel, and the system is allowed to equilibrate once again. Calculate the mass of N2O4 in the final equilibrium mixture.