In the figure shown the radius of curvature of the left `&` right surface of the concave lens are `10cm` & `15 cm` respectively. The radius of curvature of the mirror is `15 cm` . equivalent focal length of the combination is
A. the system behaves like a convex mirror of focal length `18 cm`
B. the system behaves like a concave mirror of focal length `18 cm`
C. the system behaves like a convex mirror of focal length `36 cm`
D. the system behaves like a concave mirror of focal length `36 cm`
