M and R be the mass and radius of a disc. A small disc of radius $\mathrm{R} / 3$ is removed from the bigger disc as shown in figure. The moment of inertia of remaining part of bigger disc about an axis $A B$ passing through the centre $O$ and perpendicular to the plane of disc is $\frac{4}{x} \mathrm{MR}^2$. The value of $x$ is $\underline{\hspace{2cm}}$.