Perimeter is the distance around a closed figure.

To find the cost of putting a lane around a circular table cover, we find the _____ of the table cover.

The distance around a circular region is called its _____.

If the length of a regular octagon is $4 \mathrm{cm}$, then its perimeter is _____ $\mathrm{cm}$.

The area of circular ring with outer and inner radii $\text{'}{\mathrm{r}}_1\text{'}$ and $\text{'}{\mathrm{r}}_2\text{'}$ respectively is _____.