**3. Data from Problem 1.19 (GPA): Available on Ku. Predictor variable is ACT test score. Sample size is 120 students. (a) Calculate the summary statistics (Pxi , Pyi , Px2i , Py2i , Pxiyi) using software (or your calculator), and then use them to calculate the least squares estimates by hand. State the estimated regression function. (b) Use software to plot the estimated regression function with the data points. Does it appears to fit well? (c) Obtain a point estimate of the mean freshman GPA for students whose ACT test score is 22. (d) Obtain a point estimate of the change in the mean freshman GPA for students when the ACT test score increases by 4 points.