The whole circumference is 8.556. The partial circumference is 0.250.
That gives us a proportion.
0.250 / 8.556 = 0.0292 (approximate)
This tells you that 0.250 is about 3% of the way around the circle.
How many degrees is all the way around the circle? 360.
What is about 3% of 360?
0.0292 * 360 = 10.512
Answer: About 10.5 degrees.
Short version
Circumference is 8.556, distance between two points on circumference is 0.250. How many degrees?
0.250 / 8.556 = x / 360
x = 360 * 0.250 / 8.556
x = 10.512 (approximate)
Answer: About 10.5 degrees.