Note....There are ≈ 39.37 inches to one meter
So we have
4000 = 2 * pi^2 * (.59 * 39.37) * r^2
( 4000 / [ 2 * pi^2 * (.59 * 39.37) ] ) = r^2 take the square root of both sides
2.95 in ≈ r
And there are ≈ 2.54 cm to one in
So....radius ≈ 2.54 * 2.95 ≈ 7.493 cm