A systematic sample of the number of births (in thousands) and the birth rate (in births per 1000 people) in the United States between 1950 and 1990 is given. Year 1950 1955 1960 1965 1970 1975 1980 1985 1990 Births 3632 4097 4258 3760 3731 3144 3612 3761 4158 Birth rate 24.1 25.0 23.7 19.4 18.4 14.6 15.9 15.8 16.7 a) Give an estimate of the total number of births during this period. Find a rough estimate of the variance. b) Give an estimate of the average birth rate during this period and find an appropriate estimator of the variance. Is this average a good predictor of the birth rate in 1995? Please explain