[tex]\frac{2}{7}[/tex]
1) To find the scale factor between those two triangles, we need to consider that these figures have been transformed equally, so each side of triangle XYZ was equally enlarged
2) So, let's find the scale factor by writing ratios in which the numerator presents the measure of RST and the denominator the measures of XYZ:
[tex]\frac{3}{10.5}=\frac{6}{21}=\frac{4}{14}=\frac{2}{7}[/tex]
So the scale factor is:
[tex]\frac{2}{7}[/tex]
