Metlock Corp. sold its old lunchroom refrigerator for its book value of $480 when it purchased a new refrigerator for $3,150. As a result of this purchase, employees were bringing their lunch to work more often, thus saving the company approximately $860 per year in productivity gains over the life of the fridge. Which of these amounts reflect positive cash (in)flows as opposed to negative cash (out)flows? Which cash flows should be discounted using the PV of a single sum formula, and which cash flows should be discounted using the PV of an ordinary annuity formula