Two point charges, -10nC and +16nC , are held fixed a distance 0.55m apart. Assume that both charges lie on x-axis, for the -10nC x= 0 and for the +16nC charge x= 0.55 . (a) Where can a +20nC charge be placed so that the net force on it is zero? (b) Repeat part A if the third charge is -20nC .