Southern Corporation has a capital structure of 40% debt and 60% common equity. This capital structure is expected not to change. The firm's tax rate is 21%. The firm can issue the following securities to finance capital investments:

Debt: Capital can be raised through bank loans at a pretax cost of 8%. Also, bonds can be issued at a pretax cost of 9.6%.

Common Stock: Retained earnings will be available for investment. In addition, new common stock can be issued at the market price of $64. Flotation costs will be $4 per share. The recent common stock dividend was $4.66. Dividends are expected to grow at 8% in the future.

What is the cost of external equity?