Consider the equilibrium:
2 A + B <----> 2 C
You prepare a mixture with initial concentrations [A]0 = 0.03 mol/L, [B]0 = 0.023 mol/L, and [C]0 = 0. You wait until the mixture reaches equilibrium, and then you measure the concentration of C: [C]eq = 0.013 mol/L. From your experiment compute the equilibrium constant Kc of the reaction.