Charges of 4 µC are located at x = 0, y = 2.0 m and at x = 0, y = -2.0 m. Charges Q are located at x = 4.0 m, y = 2.0 m and at x = 4.0 m, y = -2.0 m. The electric field at x = 0, y = 0 is (4 ✕ 103 N/C) i. Determine Q.

Answer 1

at (0,0) the fields from the first two charges cancel each other.

to get a field at (0,0) in the y direction the x components of charges Q must cancel.
Therefore one must be +Q and the other -Q

If the field is up (+ i direction)
the one below the axis is +Q and the one above the axis is -Q

each contributed half of the E field
distance = d = sqrt (20) = 2 sqrt 5
so d^2 = 20
E = 2 *10^3 = k Q/20

Answer 2

so Q = (2*10^3*20)/(8.99*10^9) ?
i calculated that and it doesnt give me the correct answer