Field inside a charged ball

Find the magnitude of the electric field at the center of a ball of radius $R$ with volume charge density $\rho = \vec{a}\cdot\vec{r},$ where $\vec{r}$ is the radius vector drawn from the ball's center and $\vec{a}$ is a constant vector.

$$
Details and Assumptions:

• $a$ denotes the magnitude of $\vec{a}$ .