Assume B–1 Accounting Consultants purchased a building for $435,000 and depreciated it on a straight-line basis over 40 years. The estimated residual value was $73,000. After using the building for 20 years, B–1 realized that the building will remain useful only 15 more years. Starting with the 21st year, B–1 began depreciating the building over the newly revised total life of 35 years and decreased the estimated residual value to $14,000. Record depreciation expense on the building for years 20 and 21.