The fence goes around the circumference of the circle. The radius (r) of the circle is related to the circumference (c) this way:
c = 2 π r so r = c/(2π)
Once you know the radius, you can find the area A using the formula:
A = π r2
In fact, you can substitute the first equation (the value of r) into the second and get a simpler solution in just one equation.
Stephen La Rocque>