Solution:
Provided that
[tex]\Delta ABC\sim\Delta LMN[/tex]From the similar triangles threorem, we have
[tex]\begin{gathered} \frac{AB}{LM}=\frac{BC}{MN}=\frac{AC}{LN} \\ \Rightarrow\frac{18}{6}=\frac{3}{1} \end{gathered}[/tex]Hence, the scale factor is
[tex]3[/tex]