What is the sum of the interior angles of a polygon with 5 sides?

540 degrees. Draw line segments to connect vertices and make trianlges. You will have three triangles. Since each triangle has 180 degrees and there are three of them (180 x 3) the answer is 540 degrees.

A square or rectangle has four right angles of 90 degrees each (90 x 4) and therefore it is 360 degrees. You can make two triangle when you draw a diagonal line. Each triangle is 180 degrees and equals 360 degrees.