On January 2, year 1, Lava, Inc. purchased a patent for a new consumer product for $90,000. At the time of purchase, the patent was valid for fifteen years; however, the patent's useful life was estimated to be only ten years due to the competitive nature of the product. On December 31, year 4, the product was permanently withdrawn from sale under governmental order because of a potential health hazard in the product. What amount should Lava charge against income during year 4, assuming amortization is recorded at the end of each year?