Two Infinite, Uniformly Charged, Flat Surfaces Are Mutually Perpendicular

Multiple Choice

Two infinite, uniformly charged, flat surfaces are mutually perpendicular. One of the sheets has a charge density of +60 pC/m², and the other carries a charge density of −80 pC/m². What is the magnitude of the electric field at any point not on either surface?

A) 1.1 N/C
B) 5.6 N/C
C) 7.9 N/C
D) 3.8 N/C
E) 4.0 N/C