We need to be able to calculate this, without having to consider the size of the exterior and interior angles of all the different polygons.
Let the size of an exterior angle be ##x°##
The size of the interior angle is therefore ##5x°##
An exterior and interior angle are supplementary angles.
##x° + 5x° = 180° rArr 6x = 180°##
##x = 30°## This is size of each exterior angle (##ext angle##)
The sum of the exterior angles is 360°
Number of sides (or angles) = ##360/(ext angle)##
##360/30 = 12## sides
