Prove the following

Let $\rho(\mathrm{r})=\frac{\mathrm{Q}}{\pi \mathrm{R}^{4}} \mathrm{r}$ be the charge density distribution for a solid sphere of radius $\mathrm{R}$ and total charge $\mathrm{Q}$. For a point 'p' inside the sphere at distance $r_{1}$ from the centre of the sphere, the magnitude of electric field is :-