In order to draw the ray diagram, let's draw two rays: one parallel to the lens axis, which will pass through the focus of the lens, and one passing through the center of the lens.
Drawing the ray diagram of this question, we have:
In order to calculate the magnification, first let's calculate the image position:
[tex]\begin{gathered} \frac{1}{f}=\frac{1}{d_o}+\frac{1}{d_i}\\ \\ \frac{1}{5}=\frac{1}{15}+\frac{1}{d_i}\\ \\ \frac{1}{d_i}=\frac{3}{15}-\frac{1}{15}=\frac{2}{15}=\frac{1}{7.5}\\ \\ d_i=7.5\text{ cm} \end{gathered}[/tex]The magnification is given by:
[tex]M=-\frac{d_i}{d_o}=-\frac{7.5}{15}=-0.5[/tex]
