Angles in a nonagon
A regular nonagon is a 9-sided polygon with all of its sides and angles of the same measure.
The sum of the interior angles in a n-sided polygon is:
S = 180*(n-2)
And each internal angle has a measure of:
I = S/n = 180*(n-2)/n
For n=9:
I = 180*7/9=140°
Since the sum of all exterior angles of ANY polygon is 360°, each exterior angle of a nonagon is 360/9 = 40°
Answer: Internal angle=140°. External angle=40°