A machine with a cost of $$144,000$ has an estimated residual value of $$18,000$ and an estimated life of $5$ years or $18,000$ hours. It is to be depreciated by the units$-$of$-$activity method. What is the amount of depreciation for the second full year, during which the machine was used $6,400$ hours?

a$.$ $$44,800$

b$.$ $$26,800$

c$.$ $$57,600$

d$.$ $$6,400$