Problem 3.6

A positive point charge $50 \mu \mathrm{C}$ is located in the plane $x y$ at the point with radius vector $\mathrm{r}_ {0}=2 \mathbf{i}+3 \mathbf{j},$ where $\mathbf{i}$ and $\mathbf{j}$ are the unit vectors of the $x$ and $y$ axes. Find the vector of the electric field strength $\mathbf{E}$ and its magnitude at the point with radius vector $\mathbf{r}=8 \mathbf{i}-5 \mathbf{j} .$ Here $r_{0}$ and $r$ are expressed in metres.