20? I'm not sure
An interior angle of a regular octagon is 45 degrees. The exterior angles measure 315 degrees.
The measure of the exterior angle of a convex octagon is indeterminate.
135
Providing that it is a regular octagon each interior angle measures 135 degrees
Providing that it is a regular octagon each exterior angle measures 45 degrees.
Providing that it's a regular octagon then each interior angle will measure 135 degrees.
45 degrees providing that it is a regular octagon
45 degree
1,080
135 Each interior angle of a regular octagon measures 135 degrees.
Each interior angle of a regular 8 sided octagon measures 135 degrees
Any measure that you like. There are no restrictions on an angle of an octagon, only on their sum.