Step 1:  Recall what is exterior angle

            NOTE: An exterior angle of a polygon is an angle outside the polygon    

                        formed by one of its sides and the extension of an adjacent side.

Step 2: Calculate the exterior angles of the triangle at each vertex.

              NOTE: The exterior angle theorem states that the exterior angle formed  

                           when you extend the side of a triangle is equal to the sum of its  

                           non-adjacent angles. Remember, our non-adjacent angles are  

                           those that don't touch the angle we are working with.

Step 3: Add all the exterior angles of the triangle.

            NOTE: If you count one exterior angle at each vertex, the sum of the                    

                        measures of the exterior angles of a polygon is always 360°.