Unit rate means how many necklaces in one hour if 18 take 3 hours. The answer is a third of the necklaces (6) in a third of the time (1 hr). The unit rate is 6 necklaces an hour. Since there are 60 minutes in an hour we can also say that 1 necklace takes 60/6 minutes, so the unit rate is 1 necklace in 10 minutes. It depends what you define as the unit, necklaces or time.