$${E = 2 E_{3x} = 2E_3 \cos 30^{\circ} \\ = (2) \frac{1}{4 \pi \varepsilon_0} \frac{4Q}{d^2} (0,866) = \underline{\underline{\frac{6,93Q}{4 \pi \varepsilon_0 d^2}}}}$$