18. Consider the decomposition of sulfur trioxide gas to sulfur dioxide gas and oxygen gas. Use the following data (at 25°C) to determine the temperature in °C at which standard-state equilibrium is reached for this reaction.
ΔHºf values (in kJ/mol): SO3(g), –396; SO2(g), −297; O2(g), 0
Sº values (in J/K•mol): SO3(g), 257; SO2(g), 248; O2(g), 205
(1) 272 °C (2) 198 °C (3) 448 °C (4) 786 °C (5) 912 °C
i know the answer is number 4 i just don't know why

Question

18.  Consider the decomposition of sulfur trioxide gas to sulfur dioxide gas and oxygen gas.  Use the following data (at 25°C) to determine the temperature in °C at which standard-state equilibrium is reached for this reaction.  
ΔHºf values (in kJ/mol): SO3(g),  –396; SO2(g), −297; O2(g), 0  
Sº values (in J/K•mol): SO3(g), 257; SO2(g), 248; O2(g), 205
	(1)  272 °C       (2)  198 °C       (3)  448 °C       (4)  786 °C       (5)  912 °C
i know the answer is number 4 i just don't know why