In recent years, Marigold Company has purchased three machines. Because of frequent employee turnover in the accounting department, a different accountant was in charge of selecting the depreciation method for each machine, and various methods have been used. Information concerning the machines is summarized in the table below. For the declining-balance method, Marigold Company uses the double-declining rate. For the units-of-activity method, total machine hours are expected to be 27,000. Actual hours of use in the first 3 years were 2021, 700; 2022, 4,200; and 2023, 6,200. (a1) For Bus \#3, calculate depreciable cost per mile under units-of-activity method. Depreciable cost \$1 per mile