b
\(\text { Position vector } \overrightarrow{\mathrm{r}}_{\text {COM }}=\frac{\mathrm{m}_1 \overrightarrow{\mathrm{r}}_1+\mathrm{m}_2 \overrightarrow{\mathrm{r}}_2+\mathrm{m}_3 \overrightarrow{\mathrm{r}}_3}{\mathrm{~m}_1+\mathrm{m}_2+\mathrm{m}_3}\)

\(\overrightarrow{\mathrm{r}}_{\text {COM }}=\frac{2 \mathrm{M} \times 0+2 \mathrm{M} \times 4 \hat{\mathrm{i}}+2 \mathrm{M} \times 4 \hat{\mathrm{j}}}{6 \mathrm{M}}\)

\(\overrightarrow{\mathrm{r}}=\frac{4}{3} \hat{\mathrm{i}}+\frac{4}{3} \hat{\mathrm{j}}\)

\(|\overrightarrow{\mathrm{r}}|=\frac{4 \sqrt{2}}{3}\)

\(\mathrm{x}=3\)