Ely Co. bought a patent from Baden Corp. on January 1, 2007, for $300,000. An independent consultant retained by Ely estimated that the remaining useful life is 30 years. Its unamortized cost on Baden 's accounting records was $150,000; the patent had been amortized for 5 years by Baden. How much should be amortized for the year ended December 31, 2007? The answer is $20,000 and it's $300,000/(20-5). I don't get where the (20-5) came from.