It should be Coulomb’s Law.
F = K * (q1*q2)/(r^2)
Where K is (9*10^9)
q is the charges
r is the radius between them.
When working with these, also remember to break them into the x and y component forces if there are multiple and one is at a diagonal.
After doing that, add all X and Y together, then use a^2+b^2=c^2 to get the total magnitude.
