I have a spreadsheet that looks like data below.

UPC Commission
1234 5%
4567 Not On file
8999 3%

What I need to do is do a lookup by UPC to another spreadsheet and return
the commission %. I'm only interested in doing this for the rows in which
the Commission field says "Not On file".

The spreadsheet that I am looking up the data from is called
"Commission.xls" and has the UPC in column a and the Commission in column B.
Each time I try to right a formula to do the lookup I get an error.

Any help would be great. Thanks!