1, ${F_{AC}}=k.\tfrac{\left| {q_{A}.q_{C}} \right|}{AC^{2}}=0.036 N$ ${F_{BC}}=k.\tfrac{\left| {q_{B}.q_{C}} \right|}{BC^{2}}=0.144N$$\Rightarrow F=F_{AC}+F_{BC}=0.18N$
1, ${F_{AC}}=k.\tfrac{\left| {q_{A}.q_{C}} \right|}{AC^{2}}=0.036 C$ ${F_{BC}}=k.\tfrac{\left| {q_{B}.q_{C}} \right|}{BC^{2}}=0.144C $$\Rightarrow F=F_{AC}+F_{BC}=0.18C$
1, ${F_{AC}}=k.\tfrac{\left| {q_{A}.q_{C}} \right|}{AC^{2}}=0.036
N$ ${F_{BC}}=k.\tfrac{\left| {q_{B}.q_{C}} \right|}{BC^{2}}=0.144
N$$\Rightarrow F=F_{AC}+F_{BC}=0.18
N$