It's a tablix on the outside (for the years) with a matrix inside (for the Totals by month for a single year). Because several years are in the outer tablix, there's a corresponding matrix for each value.

Here are the steps I followed to make it happen:

1. Create a report with a dataset of rental Years.

2. Add a tablix to the report surface.

3. remove all but one column.

4. remove the header cell.

5. Drop the RentalYear field into the tablix cell. (there's only one.)

6. Insert a row inside the group and below.

7. Click on the new empty cell (the bottom one).

8. Insert Subreport.

9. Subreport properties: use the Matrix report as the subreport.

10. Click parameters, add. prmCalendarYear = [RentalYear]

RUN.