Ooh! This is one thing I actually kinda remember from Geometry last year!

Okay, so the formula for the angles of an n-gon, where n is the number of sides, is (n-2)*180

That means that, for a 72-gon, the formula would be (72-2)*180

For a 19-gon, the formula would be (19-2)*180

etc.

Does that help?