In which optical instruments is a combination of lenses used?

Two lenses $A$ and $B$ having focal lengths $2.0 \,cm$ and $5.0 \,cm$, respectively, are placed $14 \,cm$ apart. Lens $A$ is placed to the left of lens $B$. An object is placed $3 \,cm$ to the left of lens $A$. The distance of the final image from lens $A$ will be:

$A$ biconvex lens is formed by using two thin planoconvex lenses,as shown in the figure. The refractive index and radius of curved surfaces are also mentioned in the figure. When an object is placed on the left side of the lens at a distance of $30 \ cm$ from the biconvex lens,the magnification of the image will be:

Find the distance of the final image from the object $O$,formed by the combination of lenses shown in the figure (in $cm$):

$A$ parallel beam of light is incident on a system of two convex lenses of focal lengths $f_1 = 20\, cm$ and $f_2 = 10\, cm$. What should be the distance between the two lenses so that the rays after refraction from both the lenses emerge as a parallel beam (in $, cm$)? (Note: The condition for the final rays to emerge parallel is that the focal point of the first lens must coincide with the focal point of the second lens).

$A$ diverging lens with a focal length magnitude of $25\ cm$ is placed at a distance of $15\ cm$ from a converging lens with a focal length magnitude of $20\ cm$. $A$ beam of parallel light falls on the diverging lens. The final image formed is: