physics electric force question?

Question

two identical small spheres of negligible mass. are separated by a centre to centre distance of 2 meters. The force between them is 6 N. calculate the charge on each sphere.

answer: 1.3 x 10^(-4)

Answer 1

Coulumbs Law
F=kq1q2/R^2 where
F -force between the charges
q1,q2 - charges
k= electrostatic constant (8.98E+9 N m2 /C^2 )
R - distance separating the cherges

assuming q1=q2
q= R sqrt( F/k)
q= 2 sqrt(6 /8.98E+9)
q=5.2 E-5 C (sorry it is not 1.3 E-4 C)