Final answer:
The subject of this question is the cost of building a factory and factors of production, focusing on depreciation methods and the long run.
Step-by-step explanation:
In this scenario, the subject is related to the cost of building a factory and factors of production. Industries bought land and built a plant years ago, and they calculate depreciation using the straight-line method for the building and declining balance for equipment.
The long run is the period when all costs are variable and a firm can build new factories and purchase new machinery. The cost of each factor of production is crucial for profitability and decision-making.