This reaction is a decomposition type, we make two compounds from one. This is the case where a single substance breaks down, producing two or more different substances. In orden to balance it we need to count.
We have 2 Al in both sides so at least it is balanced, but we have 3 C in reactant side from the carbonate and we may need 3 C in product side.
In conclussion we have 2 Al and 3 C on both sides. In reactant side we count 9 O so in product side we have 6 O from the Co₂ and 3 O from the aluminum oxide. Finally the reaction is balanced
