1. Is each inside angle of any octagon equal to 135°?
Only if it is a regular octagon. This is a octagon with all sides of equal length.
2. Is it possible for a polygon to have an interior angle greater than 180o?
Yes. This type of polygon is called a
3. How are the outside angles of a regular polygon, such as an hexagon, calculated?
The outside (exterior) angles of any polygon always add up to 360o. For a regular hexagon, each of the eight exterior angles is 360o divided by 6 = 60o.