Smith Industries is considering replacing a machine that is presently used in its production process. The following information is available:

Old machine Replacement machine

Original cost 60,000 45,000

Remaining useful life in years 5 5

Current age in years 5 0

Book Value $33,000

Current Disposal value in cash (in 5 years) $9,000

Future disposal value in cash (in 5 years)$0.00 0.00

Annual cash operating costs $8,000 $4,000

Which of the following amounts represents sunk cost?

Please show work.