I need help with cubic squares and how I add them

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

Find the measure of the interior angles of the following regular polygons: a triangle, a quadrilateral, a pentagon, an octagon, a decagon, a 30-gon, a 50-gon, and a 100-gon.

Im literally having a mental breakdown