During the current year, Danny, a calendar-year taxpayer, acquired and placed in service the following business assets: January: Delivery trucks $ 55,000 March: real estate building 150,000 used for warehouse. June: Computer system 35,000 September: Automobile 25,000 November: Office equipment 95,000 Which convention(s) is(are) used to figure Dannys depreciation for the current year and why