Theta Corporation is considering replacing an old machine with a new machine that costs $400,000, has a 9 year useful life and a $20,000 salvage value at the end of its life. If the new machine is purchased, the old machine will be sold immediately for its salvage value of $60,000. Annual cash inflows related to the new machine are $80,000 and occur evenly throughout the years. The payback period of the new machine is closest to: