A and c
Because it defines the boundaries of the system
I assume that the ball is stationary (v=0) at point B, so its total energy is just potential energy, and it is equal to 7.35 J.
At point A, all this energy has converted into kinetic energy, which is:

And since K=7.35 J, we can find the velocity, v:
The answer would be 46.482 because you multiply 18.3 by 2.54 because for every inch you get 2.54 centimeters