how many excess electrons must be placed on each of two small metal spheres placed 3.00 cm apart in a vacuum if the force of repulsion betwen the spheres is to be 0.000000008 N?

Question

how do i solve this problem??=(
help please.thx.

Use Coulomb's Law:
F = k Q^2/R^2

The force is F = 8*10^-9 N and the separation is R = 3*10^-2 m . Each sphere has the same charge, Q

Look up what k is and solve for Q. For the number of electrons N, solve
Q = N e
where e is the electron charge in Coulombs. Look that up too.