"The force between two charges is given by formula:"
F=k*(q_1*q_2)/r^2
r:"distance between two charges"
q_1:"the first charge"
q_2:"the second charge"
F_"AB":" represents the force between charges A and B"
F_"CB":"represents the force between charges C and B"
F_"AB" and F_"CB" " are opposite forces"
F_"AB"=k*((-4)*(-4))/2^2" "F_"AB"=(16*k)/4=4*k
F_"CB"=k*((-2)*(-4))/3^2=" "F_"AB"=(8k)/9
F_"net"=F_"AB"-F_"CB"
F_"net"=4*k-(8*k)/9
F_"net"=(36*k-8*k)/9
F_"net"=(28*k)/9" "k=9*10^9
F_"net"=(28*cancel(9)*10^9)/cancel(9)
F_"net"=28.10^9" N"