You can purchase an optical scanner today for $520. The scanner provides benefits worth $75 a year. The expected life of the scanner is 10 years. Scanners are expected to decrease in price by 30% per year. Suppose the discount rate is 9%. When is the best time to purchase the scanner? (Round your answer to the nearest cent.) NPV is maxinized when you wait ( years to purchase the scanner. At this date NPV will be equivalent to s today