I converted everything into decimals and went from there.
The legnth is irrelivant
we know that
Circumference=2 times pi time radius
c=40
40=2 times pi times radius
divide both sides by 2
20=pi times radius
divide both sides b pi
20/pi=radius
the radius is 20/pi cm or aproximately 6.366199048 cm
The answer to your question is 1 7/12