Assume that a company is considering purchasing a new piece of equipment for $240,000 that would have a useful life of 10 years and a salvage value of $24,000. The new equipment would cost $20,000 per year to operate and it would replace an old piece of equipment that costs $52,000 per year to operate. The old equipment currently being used could be sold for a salvage value of $40,000. The payback period for the new equipment is closest to