a
We know that magnification of telescope:

\(M =\frac{ f _{0}}{ f _{ e }}\)

The magnification of the eyepiece lens is given by:

\(M _{ e }=\frac{ f _{e}}{ f _{e}+ u }=\frac{ L _{ I }}{ L _{ O }}\)

Here, \(L _{1}\) is the length of the image and \(L _{0}\) is the length of the object.

Now for the eypiece lens, the distance of the object is \(-\left(f_{0}+f_{e}\right)\)

\(\frac{f_{e}}{f_{e}-\left(f_{0}+f_{e}\right)}=\frac{-I}{L}\)

\(\Rightarrow \frac{ f _{ e }}{ f _{0}}=\frac{I}{ L }\)

i.e \(M =\frac{ f _{0}}{ f _{ e }}=\frac{ L }{ I }\)