$21)$ A machine was purchased on April $1,2020$ for $$900,000.$ It's estimated salvage value is $$90,000$ and it's expected life is five years.

A$)$ Calculate the depreciation expense $($to the nearest dollar$)$ using each of the following methods. Remember to show your work!

a$.$ Straight$-$line for $2020$ and $2021.$

b$.$Double$-$declining balance for $2020$ and $2021$

c$.$Sum$-$of$-$the$-$year's$-$digits for $2020$ and $2021$

B$)$ Which method would result in the smallest income amount for $2020?$