Final answer:
The total electric potential energy between the charges is -63 J, as given in the question. None of the provided options match this value, indicating a possible error in the question or answer choices.
Step-by-step explanation:
The question asks about the electric potential energy between two point charges that are separated by a distance of 18 cm. The total electric potential energy of the system is given as -63 J, and the task is to identify how much potential energy is between the charges. This scenario is described by the concept of electrostatic potential energy in the context of classical physics. Since the total energy for the system is already provided (-63 J), this is the electric potential energy between these two charges. The student might be confused by the separation distance, but it doesn't play a role in determining potential energy if the total energy is already known.
No calculation is needed as the provided total electric potential energy is the answer we're looking for. Thus, the answer remains -63 J and does not match any of the provided options (a, b, c, d). It appears there is a mistake in the question because none of the options address the given value.