Something perhaps a little complicated

I'm working on a spreadsheet for the company that schedules shifts for
employees. Managers enter the times each employee is scheduled to work and
the sheet calculates the hours by and and by week. Beneath each day of the
week for each employee is a small comment section. it has been requested
that three things can happen in the comments section:

1) If PT Holiday or PT Vacation is entered, the hours for the week
automatically is 4 hours
2) If Holiday or Vacation is entered, the hours for the week automatically
is 8 hours
3) If no lunch is entered, the spreadsheet will not automatically subtract
the 30 minutes for lunch.

A few things to point out. Lunch is subtracted from the hours by
subtracting the amount is a fixed cell. The beginging and ending shift hours
are selected from a drop down menu created in data validation. They are in
15 minutes increments.

I already have a forumla setup when "No Lunch" is entered, it will not
subtract the 30 minutes for lunch break but I need to incorporate 1) and 2)
into it. Any suggestions are welcome and thanks in advance.

I assume standard hours are used and you are trying to determine variations due to leave etc. You can use 6 nested IF statements, chack if a cell is blank, part time holiday, part time vacation etc etc and put in the required value...