A firm has determined its optimal structure, which is composed of the following sources and target market value proportions.

Source of capital: Target market proportions:

Long$-$term debt $30\%$

Common stock equity $70\%$

Debt: The firm can sell a $15-$year, $$1,000$ par value, $10$ percent bond for $$1,200.$ In addition to the premium of $$200,$ a flotation cost of $3$ percent of the face value would be required.

Common Stock: A firm's common stock sells for $$100$ per share. The dividend expected to be paid at the beginning of next year is $$7.$ Its dividend payments have been growing constantly for the last five years. Four years ago, the dividend was $$5.$ It is expected that to sell, a new common stock issue must be underpriced at $$5$ per share, and the firm must pay $$3$ per share in flotation costs. Additionally, the firm has a marginal tax rate of $35$ percent.

$5)$ The firm's after$-$tax cost of debt using the close$-$form formula is $\_\_\_\_\_\_\_\_\_\_\_\_.$

$6)$ The firm's cost of a new issue of common stock is $\_\_\_\_\_\_\_\_\_\_.$

$7)$ The firm's cost of retained earnings is $\_\_\_\_\_\_\_\_\_\_\_\_.$