Respuesta :

Answer:

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.