So to do this one, you have to do the problem backwards!
The equation looks like this with everything plugged in:
272.2 = 2(3.14)r
You are looking for r, so start dividing
272.2 = 2(3.14)r
136.1 = (3.14)r
43.3 = r
Therefore the radius is about 43.3 in.
I hope I helped!