![enter image source here]
q_a=2C charge on the point of A
q_b=-3C charge on the point of B
q_c=8C charge on the point of C
k=9*10^9 (N*m^2)/C^2
"formula needed to solve this problem is Coulomb's law"
F=k*(q_1*q_2)/d^2
F: "Force between two charges acting each other"
q_1,q_2: "charges"
d:"distance between two charges"
step:1
color(red)(F_(AB))=k*(q_A*q_B)/(d_(AB)^2
color(red)(F_(AB))=9*10^9(2C*(-3C))/1^2
color(red)(F_(AB))=-54*C^2*10^9
step:2
color(blue)(F_(CB))=k*(q_C*q_B)/(d_(CB)^2
color(blue)(F_(CB))=9*10^9(cancel(8)C*(-3C))/cancel(8)^2
color(blue)(F_(CB))=-27*10^9*C^2/8
color(blue)(F_(CB))=-3,375*10^9*C^2
step:3
Delta F=color(blue)(F_(CB))-color(red)(F_(AB))
Delta F=-3,375*10^9*C^2-(-54*10^9*C²)
Delta F=-3,375*10^9*C^2+54*10^9*C^2
Delta F=50,625*10^9*C^2