Answer:
a. Straight Line Method for 2017
depreciation expense per year = ($162,702 - $17,802) / 5 years = $28,980
depreciation expense (August to December 2017) = $28,980 x 5/12 = $12,075
b. Sum-of-the-years'-digits for 2018
depreciation expense year 1 = 5/15 x $144,900 = $60,375 / 12 months = $5,031.25 per month
depreciation expense year 2 = 4/15 x $144,900 = $48,300 / 12 months = $4,025
depreciation expense January 2018 - July 2018 = $5,031.25 x 7 = $35,218.75
depreciation expense August 2018 - December 2012 = $4,025 x 5 = $20,125
depreciation expense 2018 = $35,218.75 + $20,125 = $55,343.75
c. Double-declining-balance for 2018
depreciation expense year 1 = 2 x 1/5 x $162,702 = $65,080.80 / 12 months = $5,423.40 per month
depreciation expense year 2 = 2 x 1/5 x $97,621.20 = $39,048.48 / 12 months = $3,254.04
depreciation expense January 2018 - July 2018 = $5,423.40 x 7 = $37,963.80
depreciation expense August 2018 - December 2012 = $3,254.04 x 5 = $16,270.20
depreciation expense 2018 = $37,963.80 + $16,270.20 = $54,234