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.

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).


x=12.
Side ST is 12
Step-by-step explanation:
do 21×3.14= 65.94
then divide by 2 since its a semicircle
equals: 32.97
than find perimeter altogether
21+28+28+32.97= 109.97ft
10 to the negative sixth equals 1/60, and then times 4 equals 4/60 or 1/15