On January 1, 2016, Biotek purchased a patent for a new product for $36,000. At the time of purchase, the patent was valid for 10 years; however, the patent's useful life was estimated to be only 5 years due to the competitive nature of the product. On December 31, 2018, the product is withdrawn from sale under governmental order because of an electrical hazard caused by the product. The charge against income during 2018 for this patent is?