I am having issues finding the derivation of the given equation to match that of the final derivation given. I know we need to do partial derivations, but I am lost as to how to begin and end.  We need to start with the general definition of dG with respect to T and V. Then, differentiate the first given equation for dG with respect to T and V. Essentially, we need to differentiate to solve for (dG/dT)subV and (dG/dV)subT.