In order to detemrine the sum of the interioir angle of a 14-gon, (that is, a polygon with 14 sides), use the following formula:
S = (n - 2)x 180
where n is the number of sides of a figure. In this case n = 14, then you have:
S = (14 - 2)x 180
S = (12) x 180
S = 2,160
Hence, the sum of the interior angles of a 14-gon is 2,160°