At December 31, 2005, Brown Co. had a machine with an original cost of $90,000, accumulated depreciation of $75,000, and an estimated salvage value of zero. On December 31, 2005, Brown was considering the purchase of a new machine having a five-year life, costing $150,000, and having an estimated salvage value of $30,000 at the end of five years. In its decision concerning the possible purchase of the machine, how much should Brown consider as sunk cost at December 31, 2005? A) $150,000 B) $120,000 C) $90,000 D) $15,000