To completely balance the equation, we do elemental balance. First for C, the C in the left side is 5 so there must be 5 CO2. Balancing the H, H20 must be 9/2 to balance the left side. The total O on the right is 29/2. In the left side, O2 must be 27/4. Multiplying by 4 to get whole number stoich.coeff, we get 4 C5H9O + 27O2 = 20 CO2 + 18 H2O.
