Electric Field strength between 3 charges and directions

[need_aca_help]

Homework Statement

Three point charges lie along a straight line as shown in the figure below, where
q1 = 6.36 µC, q2 = 1.57 µC and q3 = −1.82 µC.
The separation distances are d1 = 3.00 cm and d2 = 2.00 cm.
Calculate the magnitude and direction of the net electric force on each of the charges.

Homework Equations

The Attempt at a Solution

I think I have to use vectors but I don't know how...

 

[BvU]

Well, what equations do you have at hand to tackle this problem ?

 

[need_aca_help]

Well, what equations do you have at hand to tackle this problem ?

I'm not very good with electricity...

F = Eq
E = -(dv/dx)

 

[BvU]

So you still need an expression for either V or $\vec E$, right ?

 

[need_aca_help]

I have been stuck on this question making no progress. Please help me go somewhere...

 

[BvU]

http://en.wikipedia.org/wiki/Electric_field is a start. You need an expression for E with a magnitude and a direction.