A beam of light converges at a point $P$. Now a lens is placed in the path of the convergent beam $12 \mathrm{c}\mathrm{m}$ from $P$. At what point does the beam converge if the lens is a convex lens of focal length $20 \mathrm{c}\mathrm{m}$.

 A card sheet divided into squares each of size $1 \mathrm{m}{\mathrm{m}}^2$ is being viewed through a magnifying glass (a converging lens of focal length $10 \mathrm{cm}$) held close to the eye. What should be the distance between the object in and the magnifying glass if the virtual image of each square in the figure is to have an area of $6.25 \mathrm{m}{\mathrm{m}}^2$. Would you be able to see the squares distinctly with your eyes very close to the magnifier?