Final answer:
The measure of an exterior angle of a regular polygon with 19 sides is approximately 18.9 degrees.
Step-by-step explanation:
The subject of this question is geometry, and specifically deals with finding the exterior angle of a regular polygon. A regular polygon is a polygon with all sides and angles equal. The sum of the exterior angles of any polygon is always 360 degrees. Therefore, to find the measure of one exterior angle in a regular polygon with 19 sides, you divide 360 by 19. This gives you approximately 18.9 degrees, so the correct answer to this problem is option a) 18.9 degrees.
Learn more about Exterior Angles of a Polygon