Question 10 4.16 pts North Star is trying to determine its optimal capital structure, which now consists of only common equity. The firm will add debt to its capital structure if it minimizes its WACC, but the firm has no plans to use preferred stock in its capital structure. In addition, the firm's size will remain the same, so funds obtained from debt issued will be used to repurchase stock. The percentage of shares repurchased will be equal to the percentage of debt added to the firm's capital structure. (In other words, if the firm's debt-to-capital ratio increases from 0 to 25%, then 25% of the shares outstanding will be repurchased.) North Star is a small firm with average sales of $25 million or less during the past 3 years, so it is exempt from the interest deduction limitation. Its treasury staff has consulted with investment bankers. On the basis of those discussions, the staff has created the following table showing the firm's debt cost at different debt levels: