E 10-15 2018, assuming that another 40,000 tons of coal were mined. Change in Estimated Useful Life On January 1, 2017, Landon Excavation Company purchased a new bulldozer for $120,000. The equipment had an estimated useful life of 10 years and an estimated residual value of $10,000. On January 1, 2019, Landon determined that the bulldozer would have a total useful life of only 8 years instead of 10 years with no change in residual value. Landon uses straight-line depreciation. Compute depreciation expense on this bulldozer for 2017, 2018, and 2019