How do I number the lines on a report extract?

If you just want to sequentially number the lines on a report, if there are not too many columns you can make a Summary report which would break on something unique like Record ID#. So it would be a summary report in name only as each line would be a separate record. 

Then if you have a Dummy field called Line # with a formula value of 1, then you can show that on the report and set that field to be a running total down the page.