Ryota's method

[list][*]Ryota wants to see whether his method can work for other polygons. He draws the pentagon below. Use the picture to determine the sum of the measures of the interior angles of the pentagon.[br][br][/*][*]Click on "Show quadrilateral". Can you use his method for find the sum of the measures of the interior triangles of a quadrilateral?[/*][/list]

Information: Ryota's method