I will take a crack at it:
Area =Pi x r^2
Circumference =Pi x 2r, since:
x = Area
y = Circumference
[Pi r^2] + [Pi 2r] =80Pi
Solve for r:
2 π r + π r^2 = 80 π
Divide both sides by π:
r^2 + 2 r = 80
Add 1 to both sides:
r^2 + 2 r + 1 = 81
Write the left hand side as a square:
(r + 1)^2 = 81
Take the square root of both sides:
r + 1 = 9 or r + 1 = -9
Subtract 1 from both sides:
r = 8 or r + 1 = -9
Subtract 1 from both sides:
Answer: |r = 8 or r = -10(Discard)
