The area of a circle is [tex]\pi[/tex] times the squared radius of the circle,
[tex]A=\pi r^2[/tex]
You're given the diameter, which is twice the length of the radius,
[tex]d=2r\implies r=\dfrac d2[/tex]
Plugging this into the area formula gives
[tex]A=\pi\left(\dfrac d2\right)^2=\pi\dfrac{d^2}4[/tex]
The radius is 28 m, so the area is
[tex]A=\pi\dfrac{(28\text{ m})^2}4=196\pi\approx615.75\text{ m}^2[/tex]
