Struggling with some physics, (Its been over 10 years since I've done this) Most likely I'll have a bunch of questions to follow.
-
I'll assume you want to know the magnitude of the charges ..
Electric force .. F = k.q1.q2 / d² .. (k = 9.0^9 Nm²/C²)
Since q1 = q2 (= q)
F = k.q² / d²
q² = F.d² / k .. .. 1.90 x (6.90)² / 9.0^9 .. q² = 1.0^-8 .. ►q = 1.0^-4 C
Electric force .. F = k.q1.q2 / d² .. (k = 9.0^9 Nm²/C²)
Since q1 = q2 (= q)
F = k.q² / d²
q² = F.d² / k .. .. 1.90 x (6.90)² / 9.0^9 .. q² = 1.0^-8 .. ►q = 1.0^-4 C