the correct answer : 3.28k, 4.36k, 67.2; 72.7%

please show step by step

3. A piece of equipment, having a negligible salvage and scrap value, is estimated to have a service life of 10 years. The original cost of the equipment was $40,000. Determine the following: (a) The depreciation charge for the fifth year if double declining-balance depreciation is used; (b) The depreciation charge for the fifth year if sum-of-the-years-digits depreciation is used; (c) The percent of the original investment paid off in the first half of the service life using the double declining-balance method; and (d) The percent of the original investment paid off in the first half of the service life using the sum-of-the-years-digits method.