A long line carrying a uniform linear charge density + 50.0 C/m runs parallel to and 10.0

Question:

A long line carrying a uniform linear charge density + 50.0 µC/m runs parallel to and 10.0 cm from the surface of a large, flat plastic sheet that has a uniform surface charge density of -100 µC/m2 on one side. Find the location of all points where an a particle would feel no force due to this arrangement of charged objects.