Within similar triangles, the angles are the same. So, we need to look at the side lengths then.
72 to 12
66 to 11
42 to 7
In each pair of corresponding side lengths, the original side length from triangle ABC is divided by 6 (or multiplied by 1/6) to get the smaller side length on triangle DEF.
The scale factor from ABC to DEF is 1/6.
Hope this helps!
