A solid sphere of uniform density and radius $R$  applies a gravitational force of attraction equal to  $F_1$ on a particle placed at $P$, distance  $2R$ from the centre  $O$ of the sphere. A spherical cavity of radius  $\frac{R}{2}$ is now made in the sphere as shown in figure. The sphere with cavity now applies a gravitational force  $F_2$ on same particle placed at  $P$. The $\frac{F_2}{F_1}$  is  $\frac{x}{9}$. The value of  $x$ is _______.