Calculations for various depreciation methods. Assume that Gateway Motors acquires a machine for $\$ 29,600$. It expects the machine to last six years and to operate for 30,000 hours during that time. Estimated salvage value is $\$ 2,600$ at the end of the machine's useful life. Calculate the depreciation charge for each of the first three years using each of the following methods:

a. The straight-line (time) method

b. The sum-of-the-years'-digits method

c. The declining-balance method using a 33 percent rate

d. The units-of-production method, with the following operating times: first year, 4,500 hours; second year, 5,000 hours; third year, 5,500 hours