Sam & Sons Ltd. purchased machinery on September 30, 2018, at a total cost of $46,500. Sam estimated the useful life of the machinery to be eight ye or 50,000 hours, with an estimated residual value of $3,500. The machinery was used for 5,000 hours in 2018 and 12,000 hours in 2019. Calculate amortization expense for 2018 and 2019 under 1. Straight-line 2. Double-declining-balance 3. Units-of-production Round to the nearest dollar where necessary