As O2(l) is cooled at 1 atm, it freeze at 54.5 K to form Solid I. At a lower temperature, Solid I rearranges to Solid II, which has a different crystal structure. Thermal measurements show that delta H for the I --> II phase transition is -535.5 J/mol, and dela S for the same transition is - 17.0 J/K mol. At what temperature are Solids I and II in equilibrium.