A firm's stockholders expect a 10% rate of return, and there is $15M in common stock and retained earnings. The firm has $4M in loans at an average rate of 8%. The firm has raised $9M by selling bonds at an average rate of 5%. What is the firm's cost of capital:

(a) before taxes

(b) After taxes with a tax rate of 21%?

Please provide a step by step solution.