A net force of 30 N leftward is applied on a box; this net force results from a 50 N force toward the right and a 20 N force toward the left. true or false

False.

The above statement is false because force is a vector quantity, therefore when we add the force of 50 N towards the right and a 20 N force toward the left, the resultant of these forces will be (50-20) = 30 N in the direction of the major force that is Right direction.

Therefore the above statement is false, the correct statement would be net force of 30 N rightward.