Answer
Magnitude: $F=\frac{k\times6q}{d^2}$
Direction: The electrostatic force is towards the negative x direction (-i)
Work Step by Step
$F=\frac{kq_1q_2}{r^2}$
All the charges on the opposite direction towards the center particele cancel each other out except for the $+3q$
$F=\frac{k\times3q\times2q}{(d)^2} =\frac{k\times6q}{d^2} $
The electrostatic force is towards the negative x direction (-i).
