A + 35-NC Point Charge Is Placed at One Corner of a of a Square

A + 3.5-nC point charge is placed at one corner of a square (2.0 m on a side) ,and a -5.7-nC charge is placed on a corner diagonally away from the first charge.What is the magnitude of the electric field at either of the two unoccupied corners?

A) 26 N/C
B) 23 N/C
C) 18 N/C
D) 15 N/C
E) 7.6 N/C