Answer:
51°
Explanation:
the given angle of 102° is the arc angle between the 2 segment end points on the circle arc.
and this arc angle is always a seen from the center of the circle.
by moving the reference point back (to the other side of the circle) to the circle arc that angle is cut in half.
you could move that point to anywhere on the arc of the circle outside of the 2 endpoints, and the angle stays always the same.
FYI - now, if you move that point into the top half-circle between the 2 end points, the perspective flips around, and that angle becomes half of the 360-102 = 258° arc angle.