Answer:
Q E = m g electric and gravitational forces balance - both E and g are taken as positive in the downward direction
Q = m g / E = .00144 kg * 9.8 m/s^2 / 680 N/C = 2.08E-5 coul
This is the charge required for the specified force
Therefore Q = -2.08-5 C for the charge to remain stationary
