An equi-concave lens of radii of curvature of the two surfaces numerically equal to $$7\,\text{cm}$$ and refractive index $$\mu=1.5$$ has a small silver dot on the rear surface. As a result of this, a ray of light incident parallel to the principal axis gets reflected from its rear surface and then reflected also from the inner front surface. The ray after the second reflection emerges out of the thin lens and appears to focus at a point P on the principal axis. The point P lies