Final answer:
Canvas used in sails would not be considered factory overhead as it is a direct material, while the other options are related to indirect costs of manufacturing.
Step-by-step explanation:
The item that would NOT be classified as part of factory overhead of a firm that makes sailboats is c. canvas used in sails. Factory overhead costs refer to the indirect costs associated with manufacturing, which are not directly tied to the production of a specific product. Examples of factory overhead costs include costs for indirect materials, depreciation of factory buildings, and factory supplies. In contrast, the canvas used in sails is a direct material since it is a primary component of the product and can be directly attributed to the manufacturing of the sailboat.