Why does magnetic force act from a distance?

The magnetic force can act from a distance because of the magnetic field that is created around it. It can be defined as imaginary lines around the magnet upto which it has magnetic force.

If a piece of iron is put into the magnetic field but has a slight distance from the magnet, it will be pulled towards the magnet because it is in its magnetic field.

The south pole and the north poles of the magnet has effect on each other. Same poles repeal each other and opposite poles attract each other resulting in forming a field of attraction or repulsion.

The imaginary lines created are known as magnetic field which is responsible for the magnetic force from a distance.

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.