Please solve these two questions..

4. An equilateral prism deviates a ray of light through 23$°$ for two angles of incidence, which differs by
23$°$. The refractive index of prism is 
$a) \frac{\sqrt{33}}{5} b) \frac{\sqrt{43}}{5} c) 1.5 d) \frac{4}{3}$

5.  The plane side of a planoconvex lens is silvered and the lens then acts like a concave mirror of 30cm focal length. The refractive index of lens is 1.5. What is the radius of curvature of this lens?

a) 20 cm                       b) 30 cm                                  c) 40 cm                               ​     ​​d) 25 cm