posted by kim .
two small objects, A and B, are fixed in place and separated by 3.00 cm in a vacuum. object A has a charge of +2.00 micro coulomb , and object B has a charge of -2.00 micro coulomb. how many electrons must be removed from A and put onto B to make the elecrtostatic force that acts on each object an attractive force whose magnitude is 68.0 N?
Since the charges were same just opposite you can put Q1Q2 as Q^2.
Then deduct from the ansver the charge there already is and divide by elementary charge.