Complex summary on crosstab report

[sinstadt]

I need to add a summary line to a simple crosstab showing sales by financial year and category.  As well as the automated total for financial year and category, I need an additional line showing total income by current department headcount (regardless of whether they generate sales or not).  I get the full department headcount from a separate query because not all staff generate sales.
How do I create this sales per headcount calculation based on these elements of the two queries: query1.total Sales/query2.total Headcount?
thanks