The focal length of the objective lens of a compound microscope is

When can more magnification of a compound microscope be obtained?

If in a compound microscope $m_1$ and $m_2$ are the linear magnifications of the objective lens and the eye lens respectively,then the magnifying power of the compound microscope will be:

In order to increase the magnifying power of a compound microscope:

In a microscope, the objective has a focal length $f_0 = 2 \ cm$ and the eyepiece has a focal length $f_e = 4 \ cm$. The tube length is $32 \ cm$. The magnification produced by this microscope for normal adjustment is . . . . . . .

$A$ compound microscope consists of an objective lens of focal length $2 \ cm$ and an eyepiece of focal length $6.25 \ cm$ separated by a distance of $15 \ cm$. How far from the objective lens should an object be placed in order to obtain the final image at the least distance of distinct vision (in $cm$)? (Take $D = 25 \ cm$).