In recent years, Swifty 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.

$\backslash$table$[[$Bus$,$Acquired,Cost,$\backslash$table$[[$Salvage$],[$Value$]],\backslash$table$[[$Useful Life$],[$in Years$]],\backslash$table$[[$Depreciation$],[$Method$]]],[1,$Jan. $1,2020,$$$96,500,$$$5,000,4,$Straight$-$line$],[2,$Jan. $1,2020,129,000,10,000,5,$Declining$-$balance$],[3,$Jan. $1,2021,94,100,8,000,5,$Units$-$of$-$activity$]]$

For the declining$-$balance method, the company uses the double$-$declining rate. For the units$-$of$-$activity method, total miles are expected to be $123,000.$ Actual miles of use in the first $3$ years were $2021,27,500$; $2022,35,000$; 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$.$g$.0\mathrm{.}50.)$