Answer
$2.66\times 10^{-5 }\;\rm C/m^2 $
Work Step by Step
We know that the electric field at the surface of a charged conductor is given by
$$E=\dfrac{\eta}{\epsilon_0}\tag{perpendicular to surface}$$
Hence, the surface charge density is given by
$$\eta=\epsilon_0 E$$
Plugging the known;
$$\eta=(8.85\times 10^{-12})(3\times 10^6)$$
$$\eta=\color{red}{\bf 2.66\times 10^{-5}}\;\rm C/m^2 $$