... it¹

Sample calculation: in region B the field generated by the $+q$ charge at $d/2$ to its left is $k_e q/(d/2)^2 = (1/3)\times k_e 3q/(d/2)^2 = 1/3\mathrm{~of~the~unit}$ magnitude.

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... by²

To obtain this expression I took the magnitudes of the individual fields and set the signs afterward, in agreement with the direction of the fields relative to the positive direction of x-axis.

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