How would i solve for this radius?

The radius of a circleis part of the circumference formula: C = 2 pi r.
So we rearrange the formula: r = c/2 pi.
Now we have to figure out the circumference. If the outside of the circle is 12 cm for 17degrees, then17 degrees x what is 360 degrees? 360 divided by 17 is 21.2. So the 12 cm should be multiplied by 21.2, to give 254.1cm. This is our circumference.
Now we do r = 254/2 pi.
                   r = 40.46cm.

I believe it's 108x + 18