Machinery is purchased on July 1 of the current fiscal year for $240,000. It is expected to have a useful life of 4 years, or 25,000 operating hours, and a residual value of $15,000. Compute the depreciation for the last 6 months of the current fiscal year ending December 31 by each of the following methods: a. Straight-line fill in the blank 1 of 1$ b. Double-declining-balance fill in the blank 1 of 1$ c. Units-of-activity (used for 1,600 hours during the current year)