Two Charges, Find Spot of Zero Potential

[kgigs6]

Homework Statement

Charges of -q and +2q are fixed in place, with a distance d = 6.00 m between them. A dashed line is drawn through the negative charge, perpendicular to the line between the charges. On the dashed line, at a distance L from the negative charge, there is at least one spot where the total potential is zero. Find the distance L.
http://edugen.wiley.com/edugen/courses/crs1507/art/qb/qu/c19/qu_19.62.gif

Homework Equations

Vtotal = kq1/r1 + kq2/r2

The Attempt at a Solution

Since I'm looking for when vtotal = 0 then -kq/r1 = k2q/r2

I'm lost as to where to go from here, I can't figure out how to use the d=6m. Any help is appreciated!

 

[lanedance]

so find r1 in terms of r2

trhen make use fo the fact that r1, r2 & d make a right triangle