Look to the table of molar entropies provided to you.. Find the molar entropy, S for each compound at it's physical state in the reaction. Multiply by the number in the reaction, sum the products and reactants.
ΔS = S(products) - S(reactants)
ΔS = 2×(molEntropy of SO3 gas) - [2×(molEntropy of S solid) + 3×(molEntropy of O2 gas)]