3. (20 points) An experiment was conducted to test the effects of nitrogen fertilizer on lettuce production. Five rates of ammonium nitrate were applied to four replicate plots in a completely randomized design. The data are the number of heads of lettuce harvested from the plot Treatment Heads of Lettuce/plot Mean St. D. (lbs N/acre) 0 100, 120, 90, 140 1 12.50 22.1736 50 130, 135, 145, 175 146.25 20.1556 100 148, 140, 150, 158 149.00 7.3937 150 145, 160, 165, 162 158.00 8.9069 200 130, 150, 155, 160 148.75 13.1498 The following ANOVA table is obtained from SAS. Sum of Source DF Squares Mean Square F Value Pr > F Model 4939 . 300000 ? Error ? ? Corrected Total ? 8553 . 800000 (a) Fill in the missing values (indicated by "?") in the ANOVA table. (b) Test whether the nitrogen fertilizer affects the lettuce production at the 0.05 level of significance. (c) What is the estimate of the population variance