if the diameter of the cylinder's base is 8, 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=8 \end{cases}\implies V=\pi (4)^2(8)\implies V=128\pi[/tex]
