At what distance you need to place two chiseled electric charges 5nC and 6nC so that they repel

At what distance you need to place two chiseled electric charges 5nC and 6nC so that they repel each other with a force of 1.2 mN.

According to Coulomb’s law:
F = k * q1 * q2 / (r²), where F is the repulsive force of charges (F = 1.2 mN = 1.2 * 10-³ N), k is the proportionality coefficient (k = 9 * 10 ^ 9 N * m2 / Kl2), q1, q2 – charge values (q1 = 5 nC = 5 * 10 ^ -9 C, q1 = 6 nC = 6 * 10 ^ -9 C), r – distance between charges.
Distance between charges:
r = sqrt ((k * q1 * q2 / F)) = √ ((9 * 10 ^ 9) * (5 * 10 ^ -9) * (6 * 10 ^ -9) / (1.2 * 10- ³)) = √ (0.000225) = 0.015 m = 1.5 cm.
Answer: The distance is 1.5 cm.