prove that something satisfies the Gibbs/Duhem equation I have attached the one problem I need help with, along with all the information you'll need for the problem. Thanks!

Correlating VLE data to three-parameter Margules equation

Please help me with the attached problem, part (b). I have already found ln gamma1, ln gamma2, GE/RT, etc. I have plotted the experimental data. I just do not understand how to calculate A21, A12, and C of the three-parameter Margules. My professor says I can not just go in and do an Excel polynomial fit to GE/RTx1x2 and then find A21 (which is at x2=0) and A12 (which is at x1=0) that way. Because, in that case, I would not be fitting the data to the three-parameter Margules; I would be fitting the data to a whole other equation. But how do I calculate A12 and A21 by the Margules equation if at x1=0 and x2=0, GE/RT and the respective ln gammas are both undefined? I'm confused.

How much steam is required and what is the final conc of H2SO4 in tank?

How much steam is required and what is the final conc of H2SO4 in tank?

How much steam is required for each pound mass of entering acid?

How much steam is required for each pound mass of entering acid?

chemical-reaction equilibria Chapter 13 Van Ness Sixth Edition

Writing chemical-equilibrium equations for the three reactions. See attachment