Answer
$\sigma=2\times10^{-6}\frac{C}{m^2}$
Work Step by Step
We know that $E=\frac{\sigma}{\epsilon_{\circ}}$ which can be written as $\sigma=E\epsilon_{\circ}$.
Putting the values into the formula, we get
$\sigma=2.3\times10^5(8.85\times10^{-12})$
$\sigma=2\times10^{-6}\frac{C}{m^2}$