Answer: B. 45°.
Step-by-step explanation: The sum of exterior angles in a polygon is 360°. Because this is a regular polygon with eight sides all of the interior angles are equal to 180°, and cause each interior angle is supplementary to the exterior angle at the vertex. The measure of each exterior angle is equal to 45°.
(n - 2) (180°) / n (8 - 2) (180°) / 8 (6) (180°) / 8 1080 / 8 135° 180° - 135° 45°