I have a simple spreadsheet with one column showing amounts owed that I need
to bill. At the bottom of the column I sum the total amounts. In the adjacent
column I've started to put the invoice numbers for the ones that have been
billed. I'd like to write a formula that would:
Look at "column e" and
if it's not empty (meaning there's no invoice # there)
add the amount given in "column d"

This way I can subtract that total amount (which has been billed) from the
total amount owed at the bottom...that's where I would like to put the result
of this formula.

I'm sorry if I'm not explaining this well and I thank everyone for their help.