The electrostatic force of attraction between charges?

Question

of +8.0nC and -4.0nC is 2.5 x 10 to the power of -4 N.what is the distance between the charges?

Answer 1

9 * 10^9 * 8.0 * 10^(- 9) * 4.0 * 10^(- 9) / r^2 = 2.5 * 10^(- 4)

r^2 = 9 * 10^9 * 8.0 * 10^(- 9) * 4.0 * 10^(- 9) / [ 2.5 * 10^(- 4) ]

= (9 * 8 * 4 / 2.5 ) * 10^(- 5)

= 1.15 * 10^(- 3) m^2

r = 3.39 * 10^(- 2) m.

= 3.39 cm.