A vessel at

A vessel at $1000 \mathrm{~K}$ contains $\mathrm{CO}_{2}$ with a pressure of $0.5$ atm. Some of the $\mathrm{CO}_{2}$ is converted into $\mathrm{CO}$ on the addition of graphite. If the total pressure at equilibrium is $0.8 \mathrm{~atm}$, the value of $\mathrm{K}$ is :-