The magnitude of the electrostatic force between two point charges Q and q of the same sign is given by F(x) = kQq/x^2, where x is the distance between the charges and k= 9 x 10^9 N x m^2/ C^2 is a physical constant (C stands for coulomb, the unit of charge; N stands for newton, the unit of force). Find the instantaneous rate of change of the force with respect to the distance between the charges. Select the correct answer below.

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