Can someone quickly show me how to do hess law? Test in a hour 1/2!!!!?

first multiply the first equation by 1/2 and the 2nd by -1/2


2 Ba (s) + O2 (g)                     ---- > 2 BaO (s)    x 1/2           ?H = - 1107.0 kJ x 1/2
2 Ba (s) + 2 CO2 (g) + O2 (g) ---- > 2BaCO3 (g)  x-1/2        ?H = - 822.5 kJ x-1/2

Ba + 1/2 O2          -------------------------> BaO                             ?H =-553.5kJ
BaCO3                 -------------------------> Ba + CO2 + 1/2O2       ?H= 411.25kJ

and when you cross everything out I should equal BaCO3 (s) ------- > BaO (s) + CO2 (g)
 so you add up the enthalpy changes, -553.5 + 411.25 = -142.25 kJ and that should be your answer