Excel 2007 : formula help

Hi all, newbie here.
I have a spread sheet that i have been working that will track my time. My problem comes at the end ot the week. Please take a look at my problem and help...Please!

My problem is this:
It works fine until I reach 80 hrs (at which I go on OT). What I want it to do is tell the difference between my time after it reaches 80 (Straight Time st vs. Over Time ot). I can get it to calculate fine up to cell L3 but in cells K3 through O3, it should be blank and place all time in row 4. So for example, cell m3 should be blank and cell M4 should be 11. Since I could potentiall reach 80 hours after 5 or 6 days, I would like for it to calculate anytime after I reach 80. I was trying to make a formula that would work starting at cell D3 but I cant seem to wrap my head around it. it would be nice to have one formula for all cells in row 3.