Finding net electric field from three point charges

[idkwhatimdoing]

Homework Statement

The problem should be attached, not sure how to do part b.

Homework Equations

E=kQ/r^2
F=kQ1Q2/r^2
Enet=E1+E2+E3

The Attempt at a Solution

I figured out a, but have no idea how to do b. I was thinking of summing up the electric field vectors at point p, but there are 3 variables for Enet.

 

[haruspex]

I figured out a, but have no idea how to do b. I was thinking of summing up the electric field vectors at point p, but there are 3 variables for Enet.

If you sum the field vectors, how many scalar equations will you have? How many scalar unknowns are there? List them.

 

[idkwhatimdoing]

Something like this?

E1+E2+E3 = 0

kQ/16d^2 + kq2/9d^2 + kq3/25d^2(cos theta - sin theta) = 0

Not sure what to do from here though..