A charge of +24.3 µC is located at (4.40 m, 6.02 m) , and a charge of -13.1 µC is located at (-4.50 m, 6.75 m) . What charge must be located at (2.23 m, -3.01 m) if the electric potential is to be zero at the origin?

Question

A charge of +24.3 µC is located at (4.40 m, 6.02 m) , and a charge of -13.1 µC is located at (-4.50 m, 6.75 m) . What charge must be located at (2.23 m, -3.01 m) if the electric potential is to be zero at the origin? 
ANyone have any advice?

Find the distances to the center.

Potential is a scalar.

0= V1 + V2 + V3

where V1= k q1/r1 ; V2= kq2/r2 ; and V2= kq3/r3

solve for q3