d
Electric field in presence of dielectric between the two plates of a parallel plate capacitor is given by,
$E=\frac{\sigma}{K \varepsilon_{0}}$
Then, charge density
${\sigma=K \varepsilon_{0} E}$
${=2.2 \times 8.85 \times 10^{-12} \times 3 \times 10^{4} \approx 6 \times 10^{-7} \,\mathrm{C} / \mathrm{m}^{2}}$