Use Coulomb's Law to get the force exerted by one charge on the other:
F = k * q1 * q2 / d^2
F is the magnitude of the force. The direction of the force on what particle is in the opposite direction of the other particle when the charges are of the same sign.
k is Coulomb's constant--9 * 10^9 Newton meters^2 /
q1 and q2 are equal and so are 61.8 * ...
This solution calculates the magnitude of the net force on three positive particles that have charges of Q=61.8 micro coulombs, adhering to the equilateral triangle's side L=16.3cm.