Three point charges are arranged along the x-axis. charge q1 = +3 µc is at the origin, and charge q2 = "5 µc is at x = 0.200 m. charge q3 = "8 µc. where is q3 located if the net force on q1 is 7.00 n in the -x-direction?

Force on charge q1 due to charge q2 is given as

Now the net force on q1 is 7 N so the force due to q3 must be

by solving above

so q3 is at distance 0.24 m from q1

i think its

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia