Assume Z-1 Software Consultants purchased a building for $445,000 and depreciated it on a straight-line basis over 40 years. The estimated residual value was $90,000. After using the building for 20 years, Z-1 realized that the building will remain useful only 15 more years. Starting with the 21st year, Z-1 began depreciating the building over a revised total life of 35 years and decreased the residual value to $14,900. Record depreciation expense on the building for years 20 and 21.