In the given figure, the face $A C$ of the equilateral prism is immersed in a liquid of refractive index ' $n$ '. For incident angle $60^{\circ}$ at the side AC, the refracted light beam just grazes along face AC. The refractive index of the liquid $n=\frac{\sqrt{x}}{4}$. The value of $x$ is $\_\_\_\_$ . (Given refractive index of glass $=1.5$ )