A company purchased a machine for $75,000 that was expected to last 6 years and to have a salvage value of $6,000. At the beginning of the machine's fourth year the company decided that the machine's estimated useful life should be revised to a total of 10 years instead of 6 years. Also, the salvage value was re-estimated to be $5,500. Straight-line depreciation was used throughout the machine's life. Calculate the depreciation expense for the fourth year of the machine's useful life.