Buy-Rite Pharmacy has purchased a small auto for delivering prescriptions. The auto was purchased for $9,000 and will have a 6-year useful life and a $3,000 salvage value. Delivering prescriptions (which the pharmacy has never done before) should increase gross revenues by at least $5,000 per year. The cost of these prescriptions to the pharmacy will be about $2,000 per year. The pharmacy depreciates all assets using the straight-line method. what is the payback period for the auto?