13.21 In Problem 13.9 on page 440, an agent for a real estate company wanted to predict the monthly rent for one-bedroom apartments, based on the size of the apartment (stored in Silver Spring Rentals ). Using the results of that problem, a. determine the coefficient of determination, r , and interpret its meaning. b. determine the standard error of the estimate. c. How useful do you think this regression model is for predicting the monthly rent? d. Can you think of other variables that might explain the variation in monthly rent