Thank you for the opportunity to help you with your question!
30.75 kJ/deg x (33.1 - 25.6) = 230.625 kJ 230.625 kJ x 1 mol/1920 kJ = 0.120 moles 0.120 moles x 46 g/mol = 5.52 grams There is no sign for the mass of the sample. The sign for the heat of combustion would be negative (exothermic)
Please let me know if you nea case for torture by michale levined any clarification. I'm always happy to answer your questions.