I get everything up until the very end. We need to identify the bond enthalpies first: \begin{align} \ce{C=C} &= 612\\ \ce{O=O} &= 248\\ \text{SUM of these}&= 860\\ \end{align}
\begin{align} \ce{C-C} &= 348\\ 2\cdot(\ce{C-O}) &= 720\\ \text{SUM of these} &= 1068\\ \end{align} We know that enthalpy change is = products - reactants, which is $1068 - 860 = 208$, but the problem comes here: I know a minus sign is supposed to go there, but how do we know that? Exothermic reaction? Is it because of the oxygen, suggesting it's a combustion reaction or not?