(1 point) The average life expectancy in the United States, L, has been rising steadily over the past few decades, as shown in the table below. Let / be the number of years since 1920, (so t = 0 represents the year 1920, t = 10 for 1930, t = 20 for 1940, and so on). Year 1920 1930 1940 1950 1960 1970 1980 1990 (a) Find the equation of the regression line. Average life expectancy, L(t) = = Note: this is a function of t (not x). Life expectancy 56.9 61.9 63.5 67.4 69.4 72.9 74.6 78.6 (b) Estimate the average life expectancy in the United States in the year 1951 according to the linear model in part (a). Average life expectancy in 1951