Final answer:
Fixed costs, such as main office rent and field office lease payments, are constant regardless of production levels, while variable costs like utilities and salaries can fluctuate with business activity.
Step-by-step explanation:
In understanding business economics, costs are typically divided into fixed and variable costs. Fixed costs are tied to fixed inputs and do not fluctuate with the level of production. Main office costs that may not be truly fixed include utilities (as consumption can vary) and salaries if employees work overtime. On the other hand, field office costs that are fixed could include lease payments for the field office space or depreciation on field office equipment, as these remain constant regardless of the field office's output level.