Exclusion of non-working days in a report

the Customer has an activity status report with Project, PlanActivity, ResourceAssignment types. In this report, she would like to calculate durations (estimated finish - estimated start - nonworking days) and also overdue activities (today - estimated finish - nonworking days). But on report she can see total days including the nonworking days.

The Question is : how we exclude them?

Please check the attachments for more details about the report at hand.