ABC is a company listed in ASX, with its ordinary shares exhibiting the same level of systematic risk as the market portfolio. The yield on the $10-$year Australian government bond is currently $4\mathrm{.}2\%$ p$.$a$.,$ and the market risk premium is $7\%.$

Currently, ABC's shares are trading at $$7$ each, with a total of $100,000$ shares outstanding. The company has issued BB$-$rated debentures with a face value of $$300,000,$ which are currently valued at par. These debentures pay an annual coupon. With a BB credit rating, the credit spread is currently $4\mathrm{.}5\%$ p$.$a$.$ above the risk$-$free rate.

Assuming that ABC pays out all its earnings as dividends, these dividends are $100\%$ franked, with shareholders being able to utilise their franking credits fully. Assume the corporate tax rate is $28\%$

The company's cost of capital can be calculated as $\_\_\_\_\_\%.$