The precipitator uses a high voltage dc power supply to provide a set of wires with a positive charge and a set of plates with a charge.

Answer : Negative charge

Explanation :

An electrostatic precipitator is a device that is used to remove dust particles and smoke from a gas.

It consists of a stack of plates. The gas flows via the spaces between the wires. Then it passes to the stack of plates.

A high voltage power supply is applied between wires and the plates. A positive charge is applied to the set of wires and a negative charge is applied to the plates.

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.