Answer:
Sabrina owes Alexander nothing because the agreement was not in writing
Step-by-step explanation:
The reason Sabrina owes Alexander nothing is because there was no legal agreement on ground. Alexander reached this agreement with her without the both of them doing the appropriate writings, signings and documentation.
Alexander may have been able to get the courts to rule in his favor if Sabrina has tried escaping or changing the obligation they have both agreed to in writing.