Do you have a table where each record records the time worked by one employee for a period of time not greater than one day? (several per day are OK).
If so, you can set up a self join relationship that matches these records to all records by the same employee for the same week provided that you have a date field in each record that records the date for which that time was logged.
1) Define a calculation field, cWeek with this expression:
DateWorked - DayOfWeek ( DateWorked ) + 1
Select Date as the result type.
This calculates the date for Sunday of the same week so all records logged on the same week compute the same date in this field.
2) Go to Manage | Database | Relationships and add a new Tutorial: What are Table Occurrences? of your WorkLog table by selecting the existing "box" and clicking the duplicate button (two green plus signs). Link them in this type of relationship:
WorkLog::_fkEmployeeID = WorkLog 2::_fkEmployeeID AND
WorkLog::cWeek = WorkLog 2::cWeek
3) now a calculation field can be defined such as:
Sum ( WorkLog 2::Hours )
to compute the total hours worked over the bast calendar week for the employee that logged the work in the current WorkLog record.