Every shape's exterior angles must combine to form a 360* shape (meaning "full-circle" even though they are not circles). So you must divide 360 by the number of angles a shape has.
Ex #1: A Square has four angles, so the equation to finding the degrees of each exterior angle is 360/4, which equals 90. So 90* per exterior angle.
Ex #2: A Decagon has 10 angles, so the equation to finding the degrees of each exterior angle is 360/10, which equals 36. So 36* per exterior angle.
