3.50 Elephants: firstborn quadratic. Exercise 3 35 introduced you to the file ElephantsFB, which has data on 138 male African elephants that lived through droughts in the first two years of life. The variable Height records shoulder height in cm, Age is age in years, and Firstborn is 1 for firstborn and 0 for not-firstborn. IF ExpAFB a. What is the fitted quadratic regression model for using Age to predict Height? b. Now modify the model from part (a) by including an additive effect of Firstborn Is the Firstborn effect statistically significant? Interpret the coefficient of Firstborn in the context of this setting C. Is the quadratic relationship between Age and Height different for firstborn elephants than for others? Augment the model from part (b) by adding two interaction terms (one for Age . Firstborn and one for Age . Firstborn). Use a nested-models F-test to choose between this model and the part (b) model