Formula to copy in blank cells up to header

[Linda Berardo]

This is my first post so I hope I can explain. I have a worksheet and have used a macro to sum a column. I copied that formula to two columns to the right. Now, I want to use a macro to create a formula in each blank cell above the sum total. The formula would be =N33-L33. There is a header at the top.

I want to use this macro on multiple worksheets and the number of rows will vary in each worksheet. So one worksheet might be 54 rows and another might be 16 rows.