$r = \sqrt[3]{\frac{2500}{\pi}} \approx 8.6$ ft

$r = \sqrt[3]{\frac{5000}{\pi}} \approx 10.8$ ft

$r = \sqrt[3]{\frac{7500}{\pi}} \approx 12.5$ ft

$r = \sqrt[3]{\frac{10000}{\pi}} \approx 15.1$ ft