How many degrees does a 6 side polygon add up to?
Exterior angles add up to 360 degrees
Interior angles add up to 720 degrees.
The interior angles of a triangle add up to 180 degrees. Every time you add an angle, you add another 180 degrees (mark a point on a side of a polygon and call it a straight angle; that is not exactly a proof but it makes it reasonable that it is true). So the total is 180 times 2 less than the number of sides.