18.4 g of $\text{N}_2\text{O}_4$ was placed in a 1 L vessel at 400 K and allowed to attain the equilibrium $\text{N}_2\text{O}_4(g) \rightleftharpoons 2\text{NO}_2(g)$. If the total pressure at equilibrium was 10.64 bar, approximate $K_p$ is ($R = 0.083 \text{ L bar K}^{-1} \text{mol}^{-1}$). Assume $\text{N}_2\text{O}_4$ and $\text{NO}_2$ as ideal gases.