The area of a circle is given by:
[tex]A=\pi r^2[/tex]where:
[tex]\begin{gathered} r=radius=\frac{d}{2} \\ d=diameter=15ft \\ so\colon \\ r=\frac{15}{2} \end{gathered}[/tex][tex]\begin{gathered} A=\pi(\frac{15}{2})^2 \\ A=\frac{225}{4}\pi \\ A\approx176.6ft^2 \end{gathered}[/tex]