$(a)\;\large\frac{\rho_{0}}{4\in_{0}}\;(\large\frac{r}{3}-\large\frac{r^{2}}{4R})\qquad(b)\;\large\frac{\rho_{0}}{\in_{0}}\;(\large\frac{r}{3}-\large\frac{r^{2}}{4R})\qquad(c)\;\large\frac{\rho_{0}}{3\in_{0}}\;(\large\frac{r}{3}-\large\frac{r^{2}}{4R})\qquad(d)\;\large\frac{\rho_{0}}{12\in_{0}}\;(\large\frac{r}{3}-\large\frac{r^{2}}{4R})$