In order to calculate the force between the charges, we can use the formula below:

Where F is the force (in Newtons), K is the Coulomb constant (K = 9 * 10^9), q1 and q2 are the charges (in Coulombs) and d is the distance between them (in meters).
So, for q1 = q2 = 10 C and d = 12 m, we have:

Therefore the force between the charges is 6.25 * 10^9 N.