The correct answer is B. Count Related Instances.

In Workday Time Tracking, when the requirement is to determine how many holidays occur for a worker within a time week, the calculation is about counting occurrences of related records that meet certain criteria. That is exactly what Count Related Instances is designed to do. It counts the number of related objects or records associated with the parent business object, typically after applying a filter such as days marked as holidays.

In this scenario, the parent context is the time week, and the system needs to count how many related day-level instances in that week qualify as holidays. Because the requirement is a numeric count of instances, not a sum of hours or a mathematical formula, Count Related Instances is the most appropriate calculated field type.

The other options do not match the business need. Arithmetic is used when combining numeric values through math operations, but first you would still need the holiday count itself. Lookup Related Value retrieves a value from a related object, not the number of occurrences. Date Difference calculates the difference between two dates and is not intended for counting holiday days in a week.

Therefore, for calculating the number of holidays in a time week, the correct calculated field type is Count Related Instances.