posted by lisa .
A charge of -3.35 nC and a charge of -7.00 nC are separated by a distance of 40.0 cm. Find the position at which a third charge of +7.10 nC can be placed so that the net electrostatic force on it is zero.
well, it is fairly obvious a positive charge between two negatives can be placed at a zero force.
Let x be where the 3.35nC charge is.
solve for x.