Four charges are placed at the corners of a rectangle if

Question

Solve the given problem:

Problem: Four charges are placed at the corners of a rectangle. If q₁ = 43.0 x 10^-9 C, q₂ = 29.0 x 10^-9 C, q₃ = -42.0 x 10^-9 C, q₄ = -56.0 x 10^-9 C and the side of the rectangle are a = 0.31 m, and b=2a/3.

A- What would be the magnitude of the electrical field in the middle of the rectangle? Answer in units of N/C.

Please show work on how to solve! Thanks.