You can
put this solution on YOUR website!You are right about sum of exterior angles = 360 always.
a rough sketch is perhaps best way to explain external angles
draw a point,,,,and just a quadrilateral for example
pick one vertex of quadrilateral,,,, on point draw exterior angle to match.
go to next vertex,,,,draw that exterior angle on point sketch,,,(one side should match previous angle)
go to next vertex,,, draw that ext angle on point drawing
if you progress around quadrilateral,,,and mark only ext angles on point dwg,,
you should get back to beginning,,
on a point drawing if we rotate around once and come back to beginning, we go 360 degrees
the number of sides does not matter, nor does any + or - rotations, because we always go around once, and come back to beginning.