Hello!
The formula for circumference is
and the formula for area of a circle is 
. Armed with these formulas, we can begin to find the circumferences and areas of the circles.
20.
C =
C =
C =
C = 13(3.14)
C = 40.8
A =
A =
A =
A = 132.7
The circumference of the circle is 40.8 in and the area of the circle is 132.7 in².
21.
[Since we are given the diameter for this problem, to find the circumference, we no longer need to multiply the radius by 2 as in
because the diameter is the radius × 2. For we do need to divide the diameter by 2.]
C =
C = 49.3
A =
A =
A =
A = 193.5
The circumference of the circle is 49.3 in and the area of the circle is 193.5 in².
And that is all there is to it. I hope this helps you! (:
The formula for circumference is
20.
C =
C =
C =
C = 13(3.14)
C = 40.8
A =
A =
A =
A = 132.7
The circumference of the circle is 40.8 in and the area of the circle is 132.7 in².
21.
[Since we are given the diameter for this problem, to find the circumference, we no longer need to multiply the radius by 2 as in
C =
C = 49.3
A =
A =
A =
A = 193.5
The circumference of the circle is 49.3 in and the area of the circle is 193.5 in².
And that is all there is to it. I hope this helps you! (: