Final answer:
The correct 6-letter word for the costs and activities involved in maintaining something in working order is 'Upkeep'.
Step-by-step explanation:
The correct 6-letter word for the costs and activities involved in maintaining something in working order is Upkeep. Upkeep refers to the regular maintenance and repair needed to keep something in good condition.
For example, an office building requires regular upkeep to ensure that all equipment is functioning properly, the structure is well-maintained, and the overall environment is clean and presentable.
Other options such as 'Repair', 'Maintain', and 'Sustain' all relate to different aspects of keeping something in working order, but 'Upkeep' specifically encompasses the costs and activities involved in this maintenance process.