I FOUND YOUR COMPLETE QUESTION IN OTHER SOURCES.
PLEASE SEE ATTACHED IMAGE.
For this case what you should do is find the arc length.
By definition, the arc length is given by:
s = R * theta
Where,
R: radio
theta: angle
Substituting values:
s = (21) * (85 * (pi / 180))
s = 31.15412715
nearest whole number:
s = 31 inches
Answer:
C
31 inches
