Volume of a cylinder is [tex] \pi r^2h[/tex], where r is the radius and h is the height.
This comes from the area of a circle being [tex] \pi r^2[/tex]. A cylinder is the area of the base circle multiplied by its height.
Using this formula, the volume of the given cylinder is
[tex] \pi r^2(3r) \\
= 3 \pi r^3[/tex]
