Two balloons, one with a charge of 4.0 × 10-6 coulombs and the other with a charge of 8.2 × 10-6 coulombs, are kept 2.0 meters apart. what is the electric force between the two balloons? (k = 9.0 × 109newton·meter2/coulombs2) show quoted text

Force between the balloons can be calculated using Coulomb's law. Coulombs law states that the force of attraction or force of repulsion between 2 point charges is proportional to the product of the values of the charges and inversely proportional to the square of the distance between them.
F = kq₁q₂/r²
where F - force, if its 2 like charges then its force of repulsion, if its unlike charges then force of attraction 
q₁ - point charge 1 
q₂ - point charge 2 
r - distance between 2 charges 
substituting these values 

F = (4.0 × 10⁻⁶ C x 8.2 × 10⁻⁶ C x 9.0 × 10⁹ Nm²/C²) / (2 m)² 
   = 295.2 x 10⁻³ / 4
   = 7.38 x 10⁻² N

16- counting by fours