You can put this solution on YOUR website! the sum of the interior angles of any polygon are given by
(n - 2) X 180 degrees (where n is the number of sides of the polygon)
Since you have a 28 sided polygon then you get
(28 - 2) X 180 degrees
26 X 180 = 4680 degrees
Since you have a regular polygon with 28 equal sides and 28 equal angles
you divide the sum of the interior angles by 28
4680/28 = 167.14286 degrees