Answer
A hoop with the same mass and a radius $k = \sqrt{\frac{I}{M}}$ has the same rotational inertia as the given body.
Work Step by Step
Let $I'$ be the rotational inertia for the hoop.
We can find an expression for $I'$:
$I' = M~k^2$
$I' = M~(\sqrt{\frac{I}{M}})^2$
$I' = M~(\frac{I}{M})$
$I' = I$
A hoop with the same mass and a radius $k = \sqrt{\frac{I}{M}}$ has the same rotational inertia as the given body.
