We have the following:
To calculate the scale factor we must divide each of its sides, like this
[tex]\begin{gathered} \frac{4.2}{6}=0.7 \\ \frac{9.1}{13}=0.7 \\ \frac{2.8}{4}=0.7 \end{gathered}[/tex]Therefore, the scale factor that brings Triangle A to Triangle B is 0.7