During the period from 2013 to the end of 2014, Excellence, Inc. spent $90,000 on research and development for an invention that was patented on January 1, 2015. Excellence estimated that the patented invention would be useful in its production for 10 years. At the beginning of 2017, Excellence paid $16,000 in legal fees in a successful defense of the patent. What is Excellence's patent amortization expense for 2017?