The formula of the area of a circle is
[tex]A=\pi r^2[/tex]where r is the radius
in this case, we have the length of the diameter, the diameter is twice the radius
d= diameter
d=2r
therefore
r=d/2
r=8/2
r=4
we substitute the value of the radius in the formula
[tex]A=\pi r^2=\pi(4)^2=16\pi=50.27\operatorname{km}^2[/tex]the area of a circle with a diameter of 8km is 16pi km^2 or 50.27km^2
