The locks referred to here are the elevators that are used to transport boats safely from one water level to another in dams. These two varying water depths allow river traffic to operate The attached picture shows how boats enter locks in dam sites.
To regulate traffic, there are traffic lights that signal boatmen to adjust their speed when approaching the lock. The red light means to stop and to steer clear away from the lock to allows the boats inside to exit. The green light signals to enter the lock. Lastly, the amber light means approach the lock at a safe speed and under full control.
A
The horizontal force cancels out. The two 4Ns go in opposite directions. So they don't affect the outcome.
The Vertical force is 6N up - 2 N down = 4 N Up
Answer 4 N up
B
The horizontal and vertical forces cancel out. Each gives 3N - 3N =0
The net force is 0
C
You only have horizontal forces on this one
5N - 3N = 2N
The answer is 2N to the right.
Answer what? Apologies, but I don't see anything. (。>︿<)