Question

A particle with charge 8

Answer 1

he force direction is always away from a + point charge, and towards a - point charge.

Here all charges are +.

Also the third charge at x=2cm is exactly midway so r = 6cm = 0.06m in both cases.
This simplifies the maths.

At x=2 the force from the 8?C charge is to the right
Its magnitude is k.Q1.Q3/r^2 = k*8*5*10^-12 / .0036

At x=2 the force from the 3?C charge is to the left
Its magnitude is k.Q2.Q3/r^2 = k*3*5*10^-12 / .0036

So the net force is
k*(40 - 15) * 10^-12 / .0036 = 62.4 N