Delaney Company is considering replacing equipment that originally cost $$600,000$ and has accumulated depreciation of $$420,000$ to date. A new machine will cost $$790,000$ and the old equipment can be sold for $$8,000.$ The sunk cost in this situation is

$x$ a$.$ $$172,000$

$$ b$.$ $$188,000$

c$.$ $$290,000$

d$.$ $$180,000$