A company records the salaries of its employees in three classes: $20,000to$30,000 (frequency 10), $30,000to$50,000 (frequency 30), and $50,000to$80,000 (frequency 45). If a histogram is constructed where the bar for the $20,000to$30,000 class has a height of 1 unit, what should be the height of the bar for the $50,000to$80,000 class?