I need chemistry help regarding equilibrium!

The following equilibrium data are given.
HgO(s) ---> Hg(g) + ½ O2(g) ∆G⁰= -12.19 kJ at 800 K
HgO(s) ---> Hg(l) + ½ O2(g) ∆G⁰= +4.25 kJ at 800 K, ∆G⁰=-2.83 kJ at 900 K

a.) What is the value of ∆H⁰ for the reaction HgO(s) ---> Hg(l) +1/2 O2(g)

b.) What is the value of Kp at 700 K for the reaction HgO(s) ---> Hg(l) +1/2 O2(g)

c.) What is the ∆G⁰ for the vaporization of Hg(l) at 800 K? Hg(l) ---> Hg(g)