Matador Inc. purchased equipment in 2019 at a cost of $400,000. The equipment was expected to produce 500,000 units over the next five years and have a residual value of $50,000. The equipment was sold for $210,000 part way through 2021. Actual production in each year was: 2019 = 100,000 units; 2020 = 160,000 units; 2021 = 80,000 units. Matador uses units-of-production depreciation, and all depreciation has been recorded through the disposal date. Required: Calculate the gain on the sale.