Answer :

[tex]diameter=12\ ft\\\\diameter=2\ radius\\\\2r=12\ ft.\ \ \ /:2\\r=6\ ft.\\\\A=\pi r^2\\\\A=\pi\cdot6^2=36\pi\ (ft^2)\approx36\cdot3.14=113.04\ (ft^2)\approx113.0\ (ft^2)[/tex]