Assume that a machine costing $$120,000$ and having a useful life of $10$ years $($with $10000$ salvage value$).$

a$.$ Compute the depreciation expense in year $5$ by using straight$-$line

b$.$ Compute the depreciation expense in year $7$ by using sum$-$of$-$the$-$years' digits

c$.$ Compute the depreciation expense in year $3$ by using double$-$declining method