So in other words the final work done on the object would be what was initially in the system minus the other variables that took away from the system. Since there is no PE in the "final" state of the equation we don't need to worry about it because the energy that would have been used up by it...
I found the answer to this problem using the change in KE, but when I try to relate the work done on the 12.0-N block in terms of potential energy i don't get the same result. Is the change potential energy not equal to the work done? I would also like to know what situations is the change PE...