Intuit Inc. develops and sells software products for the personal finance market, including popular titles such as Quickbooks and TurboTax. Classify each of the following costs and expenses for this company as either variable or fixed to the number of units produced and sold:

a. Packaging costs
b. Sales commissions
c. Property taxes on general offices
d. Shipping expenses
e. Straight-line depreciation of computer equipment
f. Presidents salary
g. Salaries of software developers
h. Salaries of human resources personnel
i. Wages of telephone order assistants
j. Costs of providing online support
k. Users' guides