Answer:
F = - 1,598 10⁻³ N
Step-by-step explanation:
Electic strength is given by Coulomb's law
F = k q₁ q₂ / r²
Where k is the Coulomb constant that is worth 8.99 10⁸ N m²/C², q₁ and q₂ are the charges and r is the distance that separates the electric charges
In this case the charge of the two spheres is the same and of a different sign since when you remove the charge of a sphere that was initially neutral, it is left with that charge removed but of the opposite sign
q₁ = q₂ = 2.50 10¹³ electrons = 2.50 10¹³ 1.6 10⁻¹⁹
q₀ = 4.0 10⁻⁶ C
Let's calculate
F = - 8.99 10⁸ (4.0 10⁻⁶)² / 0.30²
F = - 1,598 10⁻³ N