We can find the factor of dilation by finding the ratio between two correspondent sides of the quadrilaterals.
Consider Q'R' and QR.
[tex]\begin{gathered} QR=6 \\ Q^{\prime}R^{\prime}=2 \\ \Rightarrow\frac{Q^{\prime}R^{\prime}}{QR}=\frac{2}{6}=\frac{1}{3} \end{gathered}[/tex]
Therefore, the scale factor for the dilation is equal to 1/3
