Equipment costing $80,000 with a useful life of 10 year and a residual of $8,000 has been depreciated for 6 years by the straight-line method. Assume a fiscal year ending December 31. (a) What is the book value at the end of the sixth year of use? (b) If early in the seventh year it is estimated that the remaining useful life is 5 years (instead of 4) and the residual value is $6,000, what is the amount of depreciation for the seventh year