## Algebra 1: Common Core (15th Edition)

The polygon has $9$ sides.
In order to answer the problem, we must use the formula provided and plug in the polygon's interior angle of $1260$ degrees for $s$ and derive $n$ afterward. $s=180(n−2)\\ 1260=180(n−2)\\ \frac{1260}{180}=\frac{180}{180}(n−2)\\ 7=1\cdot(n−2)\\ 7=n−2\\ 7+2=n−2+2\\ 9=n$