Answer:
12
Step-by-step explanation:
These triangles are similar using the AA theroem. This means there sides are in corresponding proportion.
Side AR and Side TE are corresponding. Use this proportion.
[tex] \frac{6}{8} [/tex]
This side the triangle SAR side lengths are 3/4 of side lengths of triangle SET.
We know that RS+ST=21
And that RS=3/4(ST).
[tex] \frac{3}{4} x + x = 21[/tex]
[tex]1.75x = 21[/tex]
x=12.
Side ST is 12
