How to highlight fields if their sum is greater than a specified value?

I have a form that I use for time tickets. It has eight fields (ST 1 - 4, and OT 1 - 4). Question 1: Is there any way that I can have all the ST fields highlight in red if the sum is greater than 8? There is no total column (and I would strongly not like to add one). Related Question 2: can I highlight all the OT fields if the sum of all eight ST and OT fields is greater than 12?

I would prefer to have them highlight as I'm entering data, but I wouldn't be opposed to a Validate button if that's easier.

Also, I have 17 rows, so is there any way to write the validation script as "this row"?

My fields are named Row1.ST1, Row 1.OT1, Row2.ST1, Row2.OT1, etc.