Hello from MrBillDoesMath!
Circumference of full circle = 2 Pi r = 2 Pi (15) = 30 Pi. As a circle contains 360 degrees, 120 degrees is one third of the circle and subtends an arc of
(30 Pi)/3 = 10 Pi
The length of an arc is, 31.41594 cm
The arc length of the circle(l) is given by:
r is the radius of the circle
is the angle in radian.
As per the statement:
For a circle with the radius of 15 cm and angle is 120 degree.
⇒r = 15 cm and angle in degree = 120
1 degree = 0.0174533 radian
120 degree = 2.094396 radian
Substitute the given values in  we have;
⇒l = 31.41594 cm
Therefore, the length of an arc is, 31.41594 cm
-6 is the correct option from the above given options