Need help with creating a measure

I have two tables:

Absence Detail which lists each planned absence an employee has requested by day (table includes date, employee, department among a few other columns.

Department Total which is a list of departments and the total employees in each.

There is a one to many relationship between DT and AD through the department.

I'm trying to develop a measure that will calculate the percentage of employees scheduled absent over the total number of employees in that particular department.

I have a Table Tile which has the Date and Department and a measure which gives me the total employees planned off for the corresponding date/department  in the table, but have had a bit of difficulty determining how to properly incorporate the department total from the DT table so I can calculate a percentage.

I got part of the Measure:  calculate(COUNTX(AD,[EmployeeNumber]))

but need to find the "divided by department total" for the % of employes planned to be out.

Once I have that my next step is to filter that calculation so that the only records that will show are those department where more than X% of their employee base is scheduled off so that the supervisor can ensure there is coverage.

I would appreciate any assistance.  I hope I have provided enough detail.  Thank you.