Electric potential at a point between 3 point charges

[Unemployed]

Homework Statement

Three pointcharges are located at the following points on an x-y coordinate system, Q1 = -3 uC at (0,0) q2 = 10.0 uc at (0,0.5m), and q3 = -3 uC at (x,0) . What is the total electric potential at the point (x/2,0) where x is in units of m. At what value does x have to be, for the potential at point (x/2,0) =0

Homework Equations

Vp =V1+v2+v3
V= k * q/r

The Attempt at a Solution

V= k([-3/(x/2)) + (10/(sq rt (.5 =(x/2)))+(-3/(x/2))

Am I going about this wrong? Should i do a vector analysis of the electric field? How do i get this to all = 0?

 

[rl.bhat]

V= k([-3/(x/2)) + (10/(sq rt (.5 =(x/2)))+(-3/(x/2))
It is wrong.
It should be
V= k([-3/(x/2)] + 10/sq rt[ (.5)^2 +(x/2)^2]+(-3/(x/2))*10^-6