Which of the following is an example of a mixed cost?

a$.$ salary of a factory supervisor

b$.$ straight$-$line depreciation on factory equipment

c$.$ rental costs of $$10,000$ per month plus $$0\mathrm{.}30$ per machine hour of use

d$.$ electricity costs of $$3$ per kilowatt$-$hour

Aal worlk saved.

As production increases, the fored cost per unit

$2.$ either increases or decreases, depending on the variable costs

b$.$ increases

c$.$ remains the same

d$.$ decreases