Identify whether each of the following is best described as a fixed, variable, or mixed cost with respect to product units.

1.	Rubber used to manufacture athletic shoes.
2.	Maintenance of factory machinery.
3.	Packaging expense.
4.	Wages of an assembly-line worker paid on the basis of acceptable units produced.
5.	Factory supervisors salary.
6.	Taxes on factory building.
7.	Depreciation expense of warehouse.