Question

Taking the first reflection of M1. If the final image coincides with s, then find n.

Answer 1

The correct answer is 150

Consider refraction on M1
$\frac{1}{V}+\frac{1}{-10}=\frac{1}{-12}$
$\Rightarrow V=60$
Now, Consider refraction from L
$\frac{1}{V}-\frac{1}{-80}=\frac{1}{-10}\Rightarrow V=\frac{80}{7}$
It is at the focus of M2,
So, $\frac{80}{7}+10=\frac{n}{7}$
$n=150$