MI about diameter $I_0 = MR²/4$. By perpendicular axis theorem, MI about center $I_c = 2I_0 = MR²/2$. By parallel axis theorem, MI about rim $I' = I_c + MR² = MR²/2 + MR² = 3MR²/2$. Since $MR² = 4I_0$, $I' = (3/2) * 4I_0 = 6I_0$.