Equipment with a cost of $$220,000$ has an estimated residual value of $$30,000$ and an estimated life of $10$ years or $19,000$ hours. It is to be depreciated by the straight$-$line method. What is the amount of depreciation for the first full year, during which the equipment was used $2,100$ hours?

$$ a$.$ $$22,000$

b$.$ $$19,000$

c$.$ $$30,000$

d$.$ $$21,000$