Exercise 2: XYZ, purchased equipment for $520,000 which was estimated to have a useful life of 10 years with a salvage value of $20,000 at the end of that time. Depreciation has been recorded for 7 years on a straight-line basis. In year 8, it is determined that the total estimated life should be 15 years with a salvage value of $10,000 at the end of that time. Compute the depreciation expense and the book value before and after change of estimations