I need with with Hess's Law. I don't understand how to use it, please help me?

Question

1. A --> B Delta H = +30 kJ
B --> C Delta H = +60 kJ

Use Hess's Law to calculate the enthaply change for reaction A --> C



2. 2H2 (g) + O2 (g) ---> 2H2O (g) Delta H = -483.6 kJ
3O2 (g) ---> 2O3 Delta H = +284.6 kJ

calculate the heat of the reaction 3H2 (g) + O3 (g) --> 3H2O (g)

Answer 1

1. by hess's law you add two rxns together B will be cancel
therefore A->C
enthapy= heat of rxn 1 + heat rxn 2= 30+60=90Kj
2.
time 3/2 to first rxn you will get
3H2+3O->3H2O and heat need to be 3/2 time also delta H
-725.4
time 1/ 2 to second rxn
3O-> O3 delta H= 142.3
flip 2nd rxn
O3->3O and delta H= -142.3
then add two rxns you will have
3H2+O3-> 3H2O
enthapy is -725.4+(-142.3)= -867.7 Kj
good luck