A truck acquired at a cost of $$80,000$ has an estimated residual value of $$8,000,$ has an estimated useful life of $200,000$ miles, and was driven $18,000$ miles during the year. Determine $($a$)$ the depreciable cost, $($b$)$ the depreciation rate, and $($c$)$ the unitsof$-$activity depreciation for the year. $($Obj$.2)$