You can directly wright down as ke*3q/2a^2 for 3q and ke*4q/a^2.-EquinoX- said:
An electric field is a force field that surrounds an electrically charged particle or object. It is created by the presence of an electric charge and can exert a force on other charged particles within its vicinity.
An electric force is the force exerted on a charged particle within an electric field. The electric field is the cause of the electric force, while the electric force is the effect of the electric field on a charged particle.
The strength of an electric field is affected by the magnitude and distance of the electric charges creating the field. The closer the charges are to each other, the stronger the electric field will be. The strength of the electric field also decreases as the distance from the charges increases.
The direction of an electric field is determined by the direction of the electric force it exerts on a positive test charge. The electric field lines point in the direction that a positive test charge would be pushed or pulled if placed in the field.
Electric fields and electric force have many practical applications, such as in electric motors, generators, and capacitors. They are also used in medical devices, such as MRI machines, and in everyday items like cell phones and computers.