if it has a diameter of 8 units, then its radius is half that, or 4.
[tex]\bf \textit{volume of a cylinder}\\\\ V=\pi r^2 h~~ \begin{cases} r=radius\\ h=height\\ \cline{1-1} r=4\\ h=20 \end{cases}\implies V=\pi (4)^2(20)\implies V=320\pi \\\\\\ V\approx 1005.309649148733\implies \stackrel{\textit{rounded up}}{V=1005}[/tex]
