Numbers pop-up cell formula

You can do something like this:

Set up you Pop-Up Menu with the work assignments.

I used A B and C but you would want to have your actual assignment names.

Make sure you select 'Start with Blank'.

With the blank selected, command-c to copy the cell, select the cells below, and command-v to paste. You will now have a column with Pop-Up Menu for each cell.

Define the row after 9:30 as a Footer Row.

Then use this formula to count the number of half-hour segments where a work assignment has been selected and multiply that by 0.5 to derive the number of hours.

=COUNTA(B)*0.5

Repeat for the other columns, replacing the B with the appropriate column letter.

SG