Find the magnitudes of the unknown forces if the sum of all forces is zero (figure)

Explanation

Let us draw the free diagram of the charge of q ( at x=0) in each case. They are shown below
`F_(1) = ( 2kq^(2))/( L^(2))- (kq^(2))/(L^(2)) = ( kq^(2))/(L^(2))` .....(i)
In case (ii), lt brgt `F_(2) = ( kq^(2))/( L^(2))` .....(ii)
In case (iii) ,
`F_(3) = (kq^(2))/( L^(2))- (kq^(2))/( L^(2)) = 0 ` ...(iii)
In case (iv) ,
`F_(4) = (3kq^(2))/( L^(2))+(kq^(2))/( L^(2)) = ( 4kq^(2))/( L^(2))`
The correct ascending order is
`implies F_(3) lt F_(1) = F_(2) lt F_(4)`