Equilibrium Constant K Problem

Question

If the combustion of C₄H_10(g) has K_200°C = 2.5x10⁴, find K_200°C for the formation of C₄H_10(g) from its elements at these conditions

Answer 1

2C₄H₁₀(g) + 13O₂(g) ==> 8CO₂(g) + 10H₂O(g) ... K = 2.5x10⁴

8CO2(g) + 10H2O(g) ==> 2C4H10(g) ... K = 1/2.5x10⁴ = 4x10^-5