Answer:
For a circle of radius R, the circumference is:
C = 2*pi*R
where pi = 3.14
And if we have an arc defined by an angle θ, the length of the arc is:
A = (θ/360°)*2*pi*R
Here we can not see the image, then i assume that B is the angle that defines the arc AC.
Now we know that the circumference is 120 in, then:
2*pi*R = 120in
Then the length of the arc is:
A = (θ/360°)*120 in
Then if the angle is 18°, we have:
A = (18°/360)*120 in = 6in