What are pecuniary costs?

Common costs are shared between the units ie departments or products. Traceable costs are specific to the unit. While I've never heard common costs being called untraceable they are cannot be...

$300

Variable costs depends on how much is used. Ex: water bill. people can have a lot or not much but depends on how much.

Overhead is considered a fixed cost, even though it may vary somewhat according to the amount of activity.

Prime cost basically is the cost of direct labor and cost of direct material; whereas conversion costs is Overhead cost and direct labor cost.