Answer:
Octagon (8-sided polygon)
- (n-2)180°
- (8-2)180°
- (6)180°
- 1080°
Nonagon (9-sided polygon)
- (n-2)180°
- (9-2)180°
- (7)180°
- 1260°
Dodecagon (12-sided polygon)
- (n-2)180°
- (12-2)180°
- (10)180°
- 1800°
Formula for sum of the interior angles:
- (n-2)180°
- n = sides of the polygon
