A machine costs $1,000, has a three-year life, and has an estimated salvage value of $100. It will generate after-tax annual cash flows (ACF) of $600 a year, starting next year. If your required rate of return for the project is 10%, what is the NPV of this investment? (Round your answer to the nearest $10.) a. $490 b. $570 c. $900 d. -$150