#### Answer

The polygon has 9 sides.

#### Work Step by Step

In order to answer the problem, you must use the formula provided and plug in the polygons interior angle of 1260 for "s", and answering for "n" afterward.
$s=180(n-2)$
$1260=180(n-2)$
$(1260)/180=(180)/180(n-2)$
$7=1(n-2)$
$7=n-2$
$7+2=n-2+2$
$9=n$