Answer :
[tex]V=\frac{ \pi }{6d^3}\\\\
Substitute\ into\ formula\ V=15000ft^3\\\\
15000=\frac{ \pi }{6d^3}\ \ |*6d^3\\\\90000d^3= \pi \ \ |:90000\\\\
d^3=\frac{ \pi }{90000}\ \ \sqrt[3]{}\\\\
d\approx0,07ft \\\\Diamater\ is\ equal\ to\ 0,07ft.[/tex]