This is the Best answer for Given the values of ΔH∘rxn, ΔS∘rxn, and T below, determine ΔSuniv.?
ΔSsurroundings = -ΔH∘rx/T
ΔSsurroundings = +84 kJ/ 395 K = 0.213 kJ/K = 212 J/K
ΔSuniverse = ΔSsystem + ΔSsurroundings
ΔSuniverse = 213 J/K + 155 J/K = 368 J/K
I believe that you probably kept the negative sign on ΔH when calculating ΔSsurroundings. Because the reaction is exothermic, that heat will increase the entropy of the surroundings, and so must have a positive value.