Skeleton equation is actually a chemical reaction whee the reactants and products are written in their chemical formula. In this problem, this is actually a combustion reaction of butane. The chemical formula for butane is C₄H₁₀.
C₄H₁₀ (l) + 6.5 O₂ (g) --> 4 CO₂ (g) + 5 H₂O (l)