An optical arrangement consists of two concave mirrors M 1 and M 2 , and a convex lens L with a common…

An optical arrangement consists of two concave mirrors $M_1$ and $M_2$, and a convex lens $L$ with a common principal axis, as shown in the figure. The focal length of $L$ is $10 \mathrm{cm}$. The radii of curvature of $M_1$ and $M_2$ are $20 \mathrm{cm}$ and $24 \mathrm{cm}$, respectively. The distance between $L$ and $M_2$ is $20 \mathrm{cm}$. A point object $S$ is placed at the mid-point between $L$ and $M_2$ on the axis. When the distance between $L$ and $M_1$ is $\frac{n}{7} \mathrm{cm}$, one of the images coincides with $S$. The value of $n$ is _____(Consider the case which gives minimum value).