8. B Company switched from the sum-of-the-years-digits depreciation method to straight-line depreciation in 2009. The change affects machinery purchased at the beginning of 2007 at a cost of $72,000. The machinery has an estimated life of five years and an estimated residual value of $3,600. What is B's 2009 depreciation expense? A. $ 8,400 B. $13,680 C. $15,840 D. $19,200 Calculations and Rationale for