Smith Industries is considering replacing a machine that is presently used in its production process. The following information is available: Original cost Remaining useful life in years Current age in years Book value Current disposal value in cash Future disposal value in cash (in 5 years) Replacement Old Machine Machine $55,000 $45,000 3 3 0 $33,000 $9,000 SO $0 8,500 $3,500 Annual cash operating costs Which of the following amounts represent a sunk cost? $33,000 $45,000 $55,000 $9,000