What you need to do is like this:
ΔSrxn∘ = Products - Reactants
ΔSrxn∘ = [NO2 (molsS∘)] - [NO (molsS∘) + O2 (molsS∘)]
ΔSrxn∘ = [(2 mol 240.0 J/molK)] - [(1 mol 205.2 J/molK) + (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
