Is My Coulomb's Law Calculation Correct?

[ForrestFire]

Homework Statement

http://i.imgur.com/ITrJq.png

Homework Equations

F=kq1q2/r^2 (Coulomb's Law)

The Attempt at a Solution

Whenever I try to get the answer, I keep coming up with 15.47cm.

I found the Coulomb's law for the third particle in relation to the other two, then set those equations to each other. This let me cancel out k and the charge of the third particle, since it wasn't given in the first place. After that it was a simple algebraic solve to find the distance.

But I feel like I'm missing something big, so I'm here for some assistance.

Thanks so much ahead of time! You guys have saved me before. It's only worth one point, which is basically nothing, but I really need to know how to do this.

 

[Spinnor]

I tried the problem, thought I had it but made a simple error, one you might be making. If you draw a picture, you might think why bother, and carefully label the forces on the third charge at some point x between the charges you might get it. Note that the forces on the third charge either both act to the left or both act to the right.

Good luck!