A 3 sided polygon (a triangle) would have angles totaling 180 degrees. So for 3, select NO.
A 4 sided polygon (a quadrilateral, like a rectangle) would have angles totaling 360. So for 4, select NO.
A 5 sided (pentagon) does total 540, so for 5, select YES.
A 6 sided (hexagon) does total 720, so for 6, select YES.