
Arturo O. answered 04/19/17
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Use Coulomb's law. Since you only want the magnitude of the force, ignore the signs of the charges.
F = kq1q2 / r122
Look up k in your physics book.
q1 = 5.8 x 105 C (By the way, there may be a typo in the problem statement. I suspect the power of 10 should really be -5.)
q2 = 4.5 x 10-5 C
r12 = (1.4 - 0) m = 1.4 m
Substitute and evaluate.