In 2015, Chris purchased a machine (7-year property) that cost $20,000 for use in his sole proprietorship. He claimed only regular MACRS depreciation (no Section 179 expensing or bonus depreciation) due to his low income that year. In 2016 and 2017 his business had operating losses and he claimed no depreciation in those years. On April 1, 2018 he sold the machine for $21,000. What is his adjusted basis for determining his gain on sale of the machine in 2018?