Find the sum of the interior angles of a polygon of $9$ sides.

Find the number of sides of a regular polygon, when its interior angle has a measure of: $135°$

Find the number of sides of a regular polygon, when its interior angle has a measure of: $120°$

Find the number of sides of a regular polygon, when its interior angle has a measure of: $170°$

Find the number of sides of a regular polygon, when its interior angle has a measure of: $168°$

Find the number of sides of a regular polygon, when its interior angle has a measure of: $175°$

Prove that the sum of all interior angles of an octagon is $1080°$.

Find the measure of each exterior angle of a regular hexagon.