Sherbrooke Cloud Services purchased a new server farm for $$250000.$ The system is expected to last six years, with a $$10000$ salvage value. Using the declining$-$balance method, determine the following: $($a$)$ The depreciation charge in year $1$; $($b$)$ The depreciation charge in year $6$; $($c$)$ The book value at the end of year $4$; $($d$)$ The accumulated depreciation at the end of year $4$