Identify fixed and variable costs 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$.$ President's salary

g$.$ Salaries of Koftware developers

h$.$ Salaries of human resources personnel

i$.$ Wages of telephone order assistants

j$.$ Costs of providing online support

k$.$ Users' guides