Resposta :
Vamos tomar os dados
8 microCoulombs = 8*10^-3 Coulombs
30cm = 0,3 metros = 3*10^-1 metros
F = k*Q^2/d^2
F= 9*10^9 * (8*10^-3)^2 / (3*10^-1)^2
F= 9*10^9 * 64*10^-6 / 9 * 10^-2
F= 10^9 * 64 *10^-6 * 10^2
F = 64 * 10^11 * 10^-6
F =64*10^5 N
8 microCoulombs = 8*10^-3 Coulombs
30cm = 0,3 metros = 3*10^-1 metros
F = k*Q^2/d^2
F= 9*10^9 * (8*10^-3)^2 / (3*10^-1)^2
F= 9*10^9 * 64*10^-6 / 9 * 10^-2
F= 10^9 * 64 *10^-6 * 10^2
F = 64 * 10^11 * 10^-6
F =64*10^5 N