A firm has the following book-value balance sheet; Debt =$ 12 ,000, Common Stock ($1 par)= 5 and Retained Earnings = $ 19 ,000. The book value of assets is the total of Debt, Common Stock and Retained Earnings. The firm's bonds are currently selling at par and the firm's stock is currently selling for $ 23 . The firm's tax rate is 40 %. What is the value of the firm's tax shield (i.e. the change in firm value due to the use of leverage in the capital structure)?