Determine whether each of the following is best described as a fixed, variable, or mixed cost with respect to product units.
1. Packaging expense.
2. Factory supervisor’s salary.
3. Taxes on factory building.
4. Depreciation expense of warehouse.
5. Rubber used to manufacture athletic shoes.
6. Maintenance of factory machinery.
7. Wages of an assembly-line worker paid on the basis of acceptable units produced.