posted by abbigail .
a charge of 7.2 nC and a charge of 6.7 nC are separated b 32 cm. Find the equilibrium position for a -3.0 nC charge.
First, see if you can get an equilibrium postition between the two charges.
Figure the force from each of the two charges, and set them equal (they will be in opposing sides, so this is valid).
K*7.2*3.0/x^2 = k*6.7*3.2/(32-x)^2
I discarded the negative signs as they are on both sides, put them in if you wish.