Twin-Cities, Inc., purchased a building for $600,000. Straight-line depreciation was used for each of the first two years using the following assumptions: 20-year estimated useful life, with a residual value of $200,000. (Marks 2)

a. Calculate the annual depreciation for the first two years that Twin-Cities owned the building.

b. Calculate the book value of the building at the end of the second year.