Step-by-step explanation:
the sum of interior angles in a triangle is 180°.
the sum of interior angles of a polygon, is the product of the number of triangles in the polygon (that can be created from a single vertex or corner via lines to all other corners) and 180°.
so, in reality, the number of triangles in each polygon is two less than the number of sides (because the lines to the 2 neighboring corners are sides and do not create triangles).
so the formula for the sum of all interior angles is
(n - 2) × 180
with n being the number of sides of the polygon.
in our case
(14 - 2) × 180 = 12×180 = 2160°
