I have a table with five columns:

Col-1: Item name
Col-2: Per unit cost
Col-3: Modifier (if cost is per-hour or per-other unit)
Col-4: Quantity
Col-5: Invoice Cost

The problem I am having is that I am trying to multiply Col-2 by Col-4 in a
field in Col-5 and I can't get it to work. I am using the "=PRODUCT(LEFT)"
formula for Col-5.

The formula does work when I put a number in Col-4, so this makes me think
the formula only works for adjacent columns.

Is there a formula I can use to acheive what I want without using literal
cell references (i.e '=PRODUCT(B2,D2)'). I can't use this because we have all
the items on the table and the salespeople just delete the ones they don't
want in there.

Thanks!