centroid of the disc

Question

A disc of radius’ r ‘has a hole of radius ‘r/2’ cut-out as shown.The centroid of the remaining disc
(shaded portion) at a radial distance from the centre “O” is

(a)$\frac{r}{2}$                                         (b)$\frac{r}{3}$
(c) $\frac{r}{6}$                                         (d)$\frac{r}{8}$