Please help me. I don’t understand this.

Answer:
Ft = 0[N]
Explanation:
To understand this problem we must perform an analysis of forces on the X axis, which coincides with the axis of forces of dogs.
In this way performing a sum of forces on the X-axis we will have (newton's third law):
[tex]F_{rigth}-F_{left}+F_{total} =0\\\ 200-200+F_{total} =0\\F_{total}=0[/tex]
From this analysis we can see that the resulting or total force is equal to zero, since there is no movement.