As shown in the figure, a block of mass $\sqrt 3 $ kg is kept on a horizontal rough surface of coefficient of friction ${1 \over {3\sqrt 3 }}$. The critical force to be applied on the vertical surface as shown at an angle 60$^\circ$ with horizontal such that it does not move, will be 3x. The value of x will be _________.

[g = 10 m/s²; sin60$^\circ$ = ${{\sqrt 3 } \over 2}$; cos60$^\circ$ = ${1 \over 2}$]