Answer :
[tex]C=2 \pi R \\ \\ C=16ft \\ \\ 2\pi R=16 => \boxed{R=\frac{16}{2\pi}=\frac{8}{\pi}} \\ \\ R=\frac{8}{\pi}=\frac{8}{3.14} \\ \\\boxed{\boxed{R \approx 2.5}}[/tex]
[tex]The\ circumference\ of\ a\ circle:C=2\pi r\ \ \ \ (r-radius)\\\\C=16ft\\\\2\pi r=16\ \ \ \ \ \ |divide\ both\ sides\ by\ 2\pi\\\\r=\frac{16}{2\pi}\\\\r=\frac{8}{\pi}\\\\we\ accept\ the\ approximation\ of\ \pi\approx3.14\\\\r=\frac{8}{\pi}\approx\frac{8}{3.14}\approx2.5\ (ft)[/tex]