Geometrical Optics

An optical arrangement consists of two concave mirrors M1 and M2, and a convex lens L with a common principal axis, as shown in the figure. The focal length of L is 10‌cm. The radii of curvature of M1 and M2 are 20‌cm and 24‌cm, respectively. The distance between L and M2 is 20‌cm. A point object S is placed at the mid-point between L and M2 on the axis. When the distance between L and M1 is ‌

n

7

‌cm, one of the images coincides with S. The value of n is__________