I'm just overly confused on how to begin this especially with the fractions... please show step by step if you could. Quiz very Soon!

Example A:

H2(g)+1/2 O2 (g) ----> H2O(l) ... ΔH= -285.8 kJ
N2O5(g) + H2O(l) -----> 2HNO3(l) ΔH= -76.56 kJ
1/2 N2(g) + 3/2 O2(g) +1/2 H2(g) -----> ΔH= -174.1 kJ

Calculate ΔH for the reaction... 2N2(g) + 5O2(g) -----> 2N2O5(g)

Example B:

Fe2O3(s)+3CO(g) -----> 2Fe(s) + 3CO2(g) ...ΔH=-28 kJ
3 Fe2O3(s) + CO(g) -----> 2Fe3O4(s) + CO2 (g) ...ΔH=-59 kJ
Fe3O4(s) +CO(g) -----> 3FeO(s) +CO2 (g) ΔH=+38 kJ

Calculate ΔH: FeO(s) + CO (g) ----->Fe(s) +CO2(g)