You can make your own: To make buttermilk, use 1 cup milk and 1 tablespoon lemon juice or white vinegar. Allow it to sit for a few minutes. If you do purchase buttermilk and have extra, freeze it in 1 cup containers or in Ziplock bags. You can also purchase powdered buttermilk in grocery stores.
Straight-line depreciation allows an equal portion of the laptop's cost to be claimed in each year over the total depreciation period. If the cost of the computer was $1,000, for example, then $200 a year can be included in the company's total depreciation amount each year for five years.
Depending on the quality of the washer/dryer I would estimate it to fully depreciate within 10 years. Ten years = 120 months. Divide the original price of the washer/dryer by 120 months to determine the depreciation each month. Then multiply by how many months the family member has had it.