A circular hole of radius \( \left(\frac{a}{2}\right) \) is cut out of a circular disc of radius ‘\( a \)’ as shown in figure. The centroid of the remaining circular portion with respect to point ‘\( O \)’ will be:
\( \frac{2}{3}a \)
\( \frac{10}{11}a \)
\( \frac{5}{6}a \)
\( \frac{1}{6}a \)