[tex]r-a\ radius\ of\ the\ circle\\\\d-a\ diameter\ of\ the\ circle\\\\a\ circumference\ of\ the\ circle:2\pi r=d\pi\\\\r=9ft\to2\pi r=2\pi\cdot9=18\pi\approx18\cdot3.14=56.52\ (in)\\\\r=21\ m\to2\pi r=2\pi\cdot21=42\pi\approx42\cdot3.14=131.88\ (m)\\\\d=30cm\to d\pi=30\pi\approx30\cdot3.14=94.2\ (cm)\\\\d=24cm\to d\pi=24\pi\approx24\cdot3.14=75.36\ (cm)\\\\r=15.2\ in\to 2\pir=2\pi\cdot15.2=30.4\pi\approx30.4\cdot3.14=95.456\ (in)\\\\r=16.01\ ft\to2\pi r=2\pi\cdot16.01=32.02\pi\approx32.02\cdot3.14=100.5428(ft)[/tex]
