Find speed of light in medium 'a' if speed of light in medium 'b' is $\large\frac{c}{3}$ where $c=$ Speed of light in vaccum and light refracts from medium 'a' to medium 'b' making $45^{\circ}$ and $60^{\circ}$ respective with normal.

Question

$(a)\;Va= \frac{\sqrt 2}{\sqrt 3}C \\ (b)\;Va= \frac{\sqrt 2}{3 \sqrt 3}C \\ (c)\;Va= \frac{3 \sqrt 2}{\sqrt 3}C \\ (d)\; Va=\sqrt {\frac{3}{2}}C$