Firm ABC is trying to estimate its optimal capital structure. Right now, Firm ABC has a capital structure that consists of $0\%$ debt and $100\%$ equity. The risk$-$free rate is $6\%$ and the market risk premium, $R_M-R_{rf},$ is $5\%.$ Currently, the company's unlevered beta is $1\mathrm{.}20$ and its tax rate is $40\%.$ What would be Firm ABC's estimated cost of equity if it were to change its capital structure to $50\%$ debt and $50\%$ equity?

$15\mathrm{.}60\%$

$13\mathrm{.}00\%$

$13\mathrm{.}64\%$

$16\mathrm{.}82\%$