An object is placed at a distance $u$ from a converging lens and its real image is received on a screen placed at a distance of $v$ from the lens. If $f$ is the focal length of the lens, then the graph between $\frac{1}{v}$ versus $\frac{1}{u}$ is:

What should be the value of distance $d$ so that the final image is formed on the object itself. (focal lengths of the lenses are as given in the figure).

Two plano-convex lenses each of focal length $10 \mathrm{cm}$ and refractive index $\frac{3}{2}$ are placed as shown in the figure. In the space left, water $\left(\mathrm{R}.\mathrm{I}.=\frac{4}{3}\right)$ is filled. The whole arrangement is in air. The optical power of the system is (in dioptre):