What you need to do is like this:
ΔSrxn∘ = Products - Reactants
ΔSrxn∘ = [NO2 (mols*S∘)] - [NO (mols*S∘) + O2 (mols*S∘)]
ΔSrxn∘ = [(2 mol * 240.0 J/mol*K)] - [(1 mol *205.2 J/mol*K) + (2 mol *210.8 J/mol*K)]
ΔSrxn∘ = [480 J/K] - [626.8 J/K]
ΔSrxn∘ = -146.8 J/K
I hope this is good for you
