Part 1 of Marshall Associates acquired a machine on January 1 at a cost of $223,600. Marshall estimates that the machine has a useful life of 9 years and a $50,800 residual value. Compute the depreciation expense for the first 2 years and determine the net book value at the end of the second year, assuming the straight-line method is used. Determine the formula to calculate the depreciation expense by using the straight-line method. Straight-line depreciation expense =