Classify each of the following as a variable or fixed cost with respect to a unit of production:

$($a$)$

Answer $1$

VariableFixed

Salaries of production supervisors

$($b$)$

Answer $2$

VariableFixed

Steel used in automobile production

$($c$)$

Answer $3$

VariableFixed

Salaries for factory custodial staff

$($d$)$

Answer $4$

VariableFixed

Depreciation of factory equipment

$($e$)$

Answer $5$

VariableFixed

Lubricants for machines

$($f$)$

Answer $6$

VariableFixed

Electricity used to operate a specific machine

$($g$)$

Answer $7$

VariableFixed

Hourly wages paid to production workers, assuming hours worked can vary

$($h$)$

Answer $8$

VariableFixed

Rent for a factory building

$($i$)$

Answer $9$

VariableFixed

Glue used in furniture production

$($j$)$

Answer $10$

VariableFixed

Maintenance for production equipment performed every month