A charge of #2 C# is passing through points A and B on a circuit. If the charge's electric potential changes from #25 J# to #18 J#, what is the voltage between points A and B?
This question goes to the very definition of electric potential.
The change in potential between two points is equal to the work done in moving the charge between these points, divided by the amount of charge.
In this case, the work done has caused a change in potential energy of the charge (as is generally the case)
The unit "joules per coulomb" is what is known as a volt.
So the potential defference is 3.5 V
Further, if we assume the charge was positive, and the potential energy decreased, then the voltage has dropped. Point B is at lower potential than point A.