Please solve attached Question.​

Q.  A circular disc of diameter d lies horizontally inside a metallic hemispherical bowl of radius 'a'. The disc is just visible to an eye looking over the edge. The bowl is now filled with a liquid of refractive index $\mu$. Now, the whole of the disc is just visible to the eye in the same position. Show that $d = 2a \left(\frac{{\mu }^2 - 1}{{\mu }^2 + 1}\right)$