a. An economist is interested in the relation between the disposable income of a family and the amount of money spent annually on food. For a preliminary study, the economist takes a random sample of eight middle-income families of the same size (father, mother two children), which is shown below. The scatter plot of the data and the resulting Excel computing output are displayed on the next page. Food expenditure y ($ 100s) 55 60 42 40 37 26 39 43 Disposable income x ($1000s) 30 36 27 20 16 24 19 25 (i) Obtain the regression equation to predict the food expenditure by the disposable income and interpret the value of the slope. (ii) Test to determine whether there is a significant positive slope. Use a = 0.05. (iii) Obtain and interpret the coefficient of determination. Suppose that the income of a family of this size is $18,000. Use the regression equation to predict the family's food expenditure