Thank you for the opportunity to help you with your question!

The quantity of triangles framed will be 2 not exactly the quantity of sides. This example is consistent for all polygons. Speaking to the quantity of sides of a polygon as n, the quantity of triangles framed is (n - 2). Since every triangle contains 180°, the total of the inside edges of a polygon is 180(n - 2)

here n=8

=180(8-2)

=1080. so A option is correct.

Please let me know if you need any clarification. I'm always happy to answer your questions.