resultant force

in question it is not specified whether all charges lie in straight line or not but for simplification we are taking them in straight line.

 

 

F_AB is the force exerted on charge at B due to charges on A.

direction is away from point A as both the charges are positive and hence their exist a repulsive force.

 

F_BC  is the force exerted on charge at B due to charge on c.

direction is away from point C as both the charges are positive and hence their exist a repulsive force.

 we can calculate these force by formula:

F = 1/4?? ( q₁*q₂/r²)

 

F_AB = 1/4?? (3q²/x²)

F_{BC  =} 1/4?? (4q²/x²)

 

and resulting force is F_R=  F_BC- F_AB = 1/4?? (4q²/x²) - 1/4?? (3q²/x²) = 1/4?? (q²/x²)

and resulting force would be towards direction of F_BC because magnitude of F_BC is greater than F_AB.