Answer
$M=+18$
Work Step by Step
See Figure 25-20. When the object and the image are both far away, the separation of the 2 lenses is the sum of their focal lengths.
The Galilean telescope is discussed on page 725. It uses a diverging lens as an eyepiece and forms upright, virtual images.
$$L=f_o+f_e$$
$$ f_e =L-f_o =36.8-39.0cm=-2.2cm$$
As expected, the diverging lens, the eyepiece, has a negative focal length.
Use equation 25-3 to find the magnification of the telescope.
$$M=-\frac{f_o}{f_e}=-\frac{39.0cm}{-2.2cm}\approx+18$$
As expected, the positive magnification means that the image is upright.