Question

what is the net force acting on the box?
20 n \t\t 27 n

what is the net force acting on the box?
78 n
5 g
78 n

which box is unbalanced?
what

Explanation:

Step1: Analyze forces in first case

Forces are in same direction. Net force is sum.
$$20 + 27$$

Step2: Calculate first net force

$$20+27 = 47\ N$$

Step3: Analyze forces in second case

Forces are in opposite directions (up - down). Net force is difference.
$$78 - 78$$

Step4: Calculate second net force

$$78 - 78=0\ N$$

Answer:

First box: $47\ N$, Second box: $0\ N$