I have been struggling all day to find the correct formula to use when trying to count unique values using different columns. I have a multiple column spreadsheet and I would like to identify the number of unique values (text & alpha) in column D (job #) that has a specific status which is in column F. For example, see below, the working status has 3 unique job#'s. Can someone help please?

Job# Status
100 Initial
201 Working
634 Working
201 Working
978 Completed
978 Working