Answer:
The total force exerted on the Y axis is: -52.07μC
Step-by-step explanation:
This is an electrostatic problem, so we will use the formulas from the Coulomb's law:

We are interested only of the effect of the force on the Y axis. We can notice that the charge placed on the x=4cm will exers a force only on the Y axis so:

Fy1=-117.61μC
For the charge placed on the origin we have to calculate the distance and the angle:

we can find the angle with:

The for the Force on Y axis is:

Fy2=65.54μC
The total force exerted on the Y axis is:
Fy=Fy1+Fy2=-52.07μC