For interior angles of regular polygons, all you have to do is add 180 degrees to the sum for each side added. For example, from triangle to quadrilateral, you would do 180 + 180 to get 360. Then from quadrilateral to pentagon, you would do 360 + 180 = 540. Do that all the way up to a heptagon and you get a sum of 900 degrees. 900 divided by seven angles will get you <u>128.57 degrees per interior angle.</u>