$r=4\, \mathrm{cm}=4 \times 10^{-2}\, \mathrm{m}$
$ \text { Potential } V =\frac{\mathrm{k} q}{\mathrm{r}} $
$=\frac{9 \times 10^{9} \times 10^{-6}}{4 \times 10^{-2}} $
$=2.25 \times 10^{5}\, \mathrm{V} $
Induced electric field $\mathrm{E}=-\frac{\mathrm{kq}}{\mathrm{r}^{2}}$
$=\frac{9 \times 10^{9} \times 1 \times 10^{-6}}{16 \times 10^{-4}}=-5.625\, \times 10^{6}\, \mathrm{V} / \mathrm{m}$




