From the calculation, we can see that the electrostatic force on the material is 1200 N.
The electrostatic force is described by Coulumb's law. According to the law;
F = Kq1q2/r^2
Where;
q1 = -4 * 10^-3 C
q2 = -3 * 10^-3 C
r = 3 m
K = 9 * 10^9
Hence
F = 9 * 10^9 * -4 * 10^-3 C * -3 * 10^-3 C/(3)^2
F = 1200 N
Learn more about coulumbs law:https://brainly.com/question/23942857
#SPJ1