A firm with a 30% marginal tax rate buys equipment for $150,000 with a salvage value of $20,000 and an expected useful life of 10 years. If the firm decides to sell the equipment after 5 years for $75,000, calculate the after-tax gain/loss on the sale of the equipment using the straight-line depreciation method. a) Zero gain/loss b) $21,000 loss c) $10,000 loss d) $7,000 loss