To answer this question, we will simply use Coulomb's which is stated as follows:
F = k*q1*q2 / r^2 where:
F is the magnitude of the force between the two charges
k is a constant = 9.00 * 10^9 N.m^2/C^2
q1 = +2.4 × 10–8 C
q2 = +1.8 × 10–6 C
r is the distance between the two charges = 0.008 m
Substituting in the equation, we get:
F = (9*10^9)(2.4*10^-8)(1.8*10^-6) / (0.008)^2 = 6.075 which is approximately 6.1 Newtons