Answer:
.00000005 C or 50 x 10^-9 C
Explanation:
Like charges REPEL
k = 8.99 x 10^9 kg m^3 / s^2 C^2 ( they should have given units of this)
F = k q1q2/r^2 q1 = q2 so
F = k q^2 / r^2
9 x 10^-3 = 8.99 x 10^9 * q^2 /.05^2 (.05 m = 5cm)
q = .00000005 C
