Question 1122010
c = 2 * pi * r


r = c / (2 * pi)


c is the circumference
r is the radius
pi = 3.121592654


when r = 5, the circumference is 2 * pi * 5 = 10 * pi = 31.41592654


when c = 31.4159, r = c / (2 * pi) = 4.999995777.


note that they used the same circumference from part b in part d except that they rounded it to 4 decimal places which is why the radius didn't come out to be exactly 5; but it was close.