Quite a simple thing, but can't work out one step.
Charge √3Q is at cartesian point (3a, a, 2a). Calculate the electric field at the point (2a, 2a, 3a) due to this charge.
using the formula;
E(r) = q / 4 ∏ ε0 |r - r0|3 (r - r0)
r = (2a ex + 2a ey + 3a ez)
r0 = (3a ex + a ey + 2a ez)