Express the equilibrium constant for the combustion of propane in the balanced chemical equation c3h8(g)+5o2((g)+4h2o(g)

According to the balanced equation:
C3H8(g) + 5O2(g) ↔ 3CO2(g) + 4 H2O (g)
      aA    + bB        ↔  cC          +    dD

according to K formula when:
K = concentration of the products / concentration of the reactants

   K = [C]^c[D]^d / [A]^a[B]^b
when [A],[B],[C]and[D] is the concentrations 
and a,b,c and d is the no of moles
∴ K = [CO2]^3[H2O]^4 / [C3H8] [ O2]^5