Answer:
9 sides
Explanation:
Sum of the measures of the interior angle of a polygon with n sides:
(n - 2)180
Measure of 1 interior angle of a regular polygon of n sides:
(n - 2)180/n
Sum of the measures of the exterior angles of a polygon, one per vertex:
360
Measure of 1 exterior angle of a regular polygon of n sides:
360/n
(n - 2)180/n = 360/n + 100
Multiply both sides by n.
(n - 2)180 = 360 + 100n
Distribute on left side.
180n - 360 = 360 + 100n
Subtract 100n from both sides.
80n - 360 = 360
Add 360 to both sides.
80n = 720
Divide both sides by 80.
n = 9
Answer: 9 sides