Final answer:
The straight-line depreciation method is suitable for assets that are similar and share the same useful lives, dividing the asset's cost evenly over its lifespan.
Step-by-step explanation:
The straight-line depreciation method should be used when the assets are similar in nature and have the same useful lives. This method spreads the cost of the asset evenly over its useful life.
For example, if an asset costs $5000 with a salvage value of $500 and a useful life of 9 years, the annual depreciation expense would be ($5000 - $500) / 9 = $500 per year.