The life expectancies (in years) for men and women in the U. S. can be given using models in slope-intercept form. Women: L = m t + b Men: L = m t + b where t is the number of years since 1980. Suppose that in 1980, women's life expectancy was 77.2 and was increasing by 0.09 years of life expectancy per year of time. (In other words, each year that passed saw women's life expectancy go up an additional 0.09 years.)