\(F _{ BC }=\frac{ K (2 q )(2 q )}{\left(\frac{ R }{4}\right)^2}=\frac{64 Kq ^2}{ R ^2}\)
\(F _{ B }= F _{ BC }- F _{ BA }=\frac{544 Kq ^2}{9 R ^2}\)
\(=\frac{544 \times 9 \times 10^9 \times\left(2 \times 10^{-6}\right)^2}{9 \times\left(2 \times 10^{-2}\right)^2}=5440\,N\)