Final answer:
Sales and Distribution should be prioritized for system implementation.
Step-by-step explanation:
In order to determine the functional area that should be prioritized for system implementation, Apex Vacuum needs to consider the area that will have the most significant impact on cost-effectiveness and future growth. Among the options provided, Sales and Distribution should be prioritized for system implementation. By implementing a system to optimize nationwide sales operations, Apex Vacuum can improve efficiency, increase sales, and expand its reach across the country.