ye thats wrong, i am guessing you went wrong by using the mass wrong in q=mc(d)t - the mass was the mass of water (100g) then 38 temp with 4.18 when you have that value you divide by a thousand to get kJ mol-1. Then you get the moles by taking away the original mass of the substance and after combustion and divide that by the Mr (Mr use your periodic table). Then you use q/n and plug in the values and then you change the sign if needed depending on if its exothermic or endothermic.