Just try to find how you will get the reaction by adding the other reactions. Reverse the second eq as O is in reactant side and half it..
Now in the final reaction there is neither ozone nor oxygen so now you have oxygen on the products side after adding reversed
2 and 3, O ->1/2 O2
adding this to the third eq you get,
NO+O +O3 -> NO2 +3/2 O2
Now you need to remove O3 and O2 using the first equation,
So reverse the first one,half it and add, 3/2O2-> O3 adding it removes O3 and O2 you get the requires equation,
NO + O->NO2 you can do the calculation bit yourself when you add reactions Enthalpy is also added by Hess law so yeah that part should be pretty simple.
