Hello there,
It will be easier if you draw the diagram first. Read the question, draw the diagram accordingly. It will be helpful.


Now let's solve the problem:

Let us assume that,
Distance between Q and +e = d
Distance between Q and -e = X-d

Force of attraction due to -e = K*{(Qe)/X-d}
Force of attraction due to +e = K*{(Qe)/d}
Here, K= 1/(4Eo)

Now, these are in equilibrium. Then,
K*{(Qe)/X-d}= K*{(Qe)/d}
Or, X-d = d
Or, 2d = X
Or, d = X/2

Hence, the charge Q should be placed at X/2 position from +e, which means exactly in the middle of the two charges given initially.


Hope this answer helps you.
Thank you!!