Question

A box that is sitting against a wall has a mass of 5 kg. The box is pushed with a force of 10 N to the left, but the box does not move. Calculate the net force acting on the box

Answer 1

The net force acting on the box is zero.

In fact, the box does not move. According to Newton's second law, this means the resultant of the forces acting on the object is zero, because the acceleration of the object is zero:
$\sum F = ma = 0$
This also means that the reaction of the wall against the box is equal to the force of 10 N that pushes the box, in order to balance it and have a net force of zero. On the vertical axis instead, the weight of the box (mg) is balanced by the normal reaction of the floor.