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

$\backslash$table$[[1.$ Rubber used to manufacture athletic shoes.,Variable$],[2.$ Salesperson salary plus commission.,$],[3.$ Packaging expense.,Variable$],[4.$ Depreciation expense of warehouse.,Fixed$],[5.$ Factory rent.,$],[6.$ Taxes on factory building.,Fixed$],[7.$ Hourly wages of assembly$-$line worker.,$]]$