In a circle, an arc has an arc length of 4π. If the arc measure is 80°, what is the length of the radius of the circle?

9 units.

Step-by-step explanation:

Arc length = r C where r = radius and C is the arc measure in radians.

Arc measure = 80 * π/180 radians. So:

4π = r * 80π/180

4 = 80r / 180

80r = 4 * 180

r = 720 / 80

r = 9.