A force of 480 N is applied to a stationary wooden box in one direction and an 920 N horizontal force is applied in the opposite direction. What additional force is necessary for the box to remain stationary?

Answer 1

Assuming zero friction, the additional force is the equilibrant.
We have a force of +480 N and -920 N.
The equilibrant is the negative of the vector sum, namely
-(480-920)=440 N, i.e. 440 N in the same direction as the 480N force.

If friction is present, some additional steps are required.