How Do You Balance Forces in a Charged Rhombus?

[kokoman]

Hello, please help me solve this so I can learn from it.

Image:
http://i48.tinypic.com/30k8y10.jpg

Two charges with charge +Q are placed at A and C vertices of a rhombus with four even sides (α).
A prticle with mass m and charge -Q is placed at vertex B.
An unknown charge size of q is placed at vertex D.
The sharp angle of the rhombus is 60 degrees.

1)
What is the size of charge q, that is suffiecient to make the electrical charge affecting the -Q charged particle at vertex B to be 0?

If charge q is removed, and the particle at vertex B is released from being stationary, while the charges at vertice A and C are still held in place.
2)
What is the initial acceleration of the released particle?
3)
What is the velocity of the particle upon reaching the center of the rhombus?

I have no much of an attempt at solution for I'm am unsure of where to start.

Thank you very much!

 

[ap123]

For (1) start by drawing all the force vectors acting on the charge at B and adding them.