As shown in the figure, a block of mass $\sqrt{3} \mathrm{~kg}$ is kept on a horizontal rough surface of coefficient of friction $\frac{1}{3 \sqrt{3}}$. The critical force to applied on the vertical surface as shown at an angle $60^{\circ}$ with horizontal such that it does not move, will be $3 x$. The value of $x$ will be $\left[g=10 \mathrm{~m} / \mathrm{s}^2 ; \sin 60^{\circ}=\frac{\sqrt{3}}{2}\right.$; $\left.\cos 60^{\circ}=\frac{1}{0}\right]$