9 - 6 = 3
so 3 + 6 = 9 which is an addition equation that helps you find the answer.
Check the picture below.
notice the solid circle at -4 and 3, since it includes those points.
also notice the dashed line, though the lines keeps on going those ways, is not included in the piece-wise, since it's not part fo the domain or constraints.
Area = pi*r^2
Circumference = 2pi*r
Step 1: find the radius from area
81pi=pi*r^2
81=r^2
9=r
Step 2: plug in radius to the circumference equation
Circumference = 2pi*r
18pi is the answer, otherwise know as 56.52 as well.
Let's say "c" is a constant, hmmmm any constant, for any value whatsoever of "x", "y" is always that constant, for example, say c = 3, thus y = 3, so a table for it will look like

now, if you plot those points, it'd looks like the picture below.