Draw the tank
we can use the formula of the volume of a cylinder
[tex]V=\pi\times r^2\times h[/tex]we can repalce the value of the volume (320pi) and the height
[tex]\begin{gathered} 320\pi=\pi\times r^2\times20 \\ 320\pi=20r^2\pi \end{gathered}[/tex]now solve for r^2 dividing 20pi on both sides
[tex]\begin{gathered} \frac{320\pi}{20\pi}=r^2 \\ \\ r^2=16 \\ \end{gathered}[/tex]and solve for r using roots
[tex]\begin{gathered} r=\sqrt[]{16} \\ \\ r=4 \end{gathered}[/tex]the value of the radious is 4ft and the diameter double, then
[tex]\begin{gathered} d=2\times4 \\ d=8 \end{gathered}[/tex]diameter of the cylinder is 8 ft then rigth option is C
