ABCDEFGH is a regular octagon. The minimum degree of rotation by which this octagon can map onto itself is °. It will take increments of that degree of clockwise rotation for A′ (the image of A) to coincide with C.
See if this helps: Interior angle for a polygon = ( n-2) *180 /n for octagon this equals 135o
EXTERIOR angle for the octogon is then 180 - 135 = 45o