In recent years, Riverbed Transportation purchased three used buses. Because of frequent turnover in the accounting department, a different accountant was in charge of selecting the depreciation method for each bus, and various methods have been used. Information concerning the buses is summarized in the table below. For the declining-balance method, the company uses the double-declining rate. For the units-of-activity method, total miles are expected to be 125,000 . Actual miles of use in the first 3 years were 2021, 25,500;2022,34,500; and 2023, 30,000 . (a1) For Bus \#3, calculate depreciation expense per mile under units-of-activity method. (Round answer to 2 decimal places, e. 9.50.) Depreciation expense $ per mile