Perdue Company purchased equipment on April $1$ for $$76,680.$ The equipment was expected to have a useful life of $3$ years, or $6,480$ operating hours, and a residual value of $$2,160.$ The equipment was used for $1,200$ hours during Year $1,2,300$ hours in Year $2,1,900$ hours in Year $3,$ and $1,080$ hours in Year $4.$

Required:

Determine the amount of depreciation expense for the years ended December $31,$ Year $1,$ Year $2,$ Year $3,$ and Year $4,$ by $($a$)$ the straight$-$line method, $($b$)$ the units$-$of$-$activity method, and $($c$)$ the double$-$declining$-$balance method.