There are 720 degrees in a 6 sided polygon.
The degrees in a 19 sided polygon add up to 3,060 degrees
The interior angles of a fifteen sided polygon amount to 2340 degrees.
1800 degrees (that is the sum of the internal angles of the 12-sided polygon).
The interior angles of a 13 sided polygon add up to 1980 degrees
2340 degrees would be in a 16 sided polygon.
The sum of the exterior angles of a polygon, however many sides it has, is 360 degrees. If the 20 sided polygon is regular, its angles are equal, and each is then 360/20 = 18 degrees.