13. The sales manager of a large sporting goods store has recently started a national advertising campaign. He has kept a record of the monthly costs of the advertising and the monthly profits. These are shown here. The entries are in thousands of dollars Month Jan. Feb. Mar. Apr. May Jun. Jul. Monthly Advertising 10.0 14.0 11.4 15.6 16.8 11.2 13.2 Cost Monthly 125 200 160 150 210 110 125 a. Assuming a linear relationship exists; derive the least-squares regression line for predicting monthly profits from monthly advertising costs. b. In August, the manager plans to spend $17,000 on advertising. Based on the data, how much profit should he expect that month? (Round to the nearest $1000.) c. Given the relationship shown by the paired scores, can you think of a reason why the manager doesn’t spend a lot more money on advertising?