A firm is considering replacing a machine that has been used to make a certain kind of packaging material. The new, improved machine will cost $31,000 installed and will have an estimated economic life of 10 years, with a salvage value of $2,500. Operating cost are expected to be $1,000 per year throughout the service life of the machine. The old machine (still in use) had an orginal cost of $25,000 four years ago, and at the time it was purchased, its service life was estimated to be seven years, with a salvage value of $5,000. The old machine, its updated market values and operating costs for the next four years is as follows: Operating EOY MV BV Costs 0 $7,700 $7,889 1 $4,300 $5,578 $3,200 2 $3,300 $3,347 $3,700 3 $1,100 $1,116 $4,800 4 $0 $0 $5,850 The firm's MARR is 12%. What is the EUAC of the Challenger? a. $6.435 b. $6,344 c. $6,789 d. $6,420