A firm with a D $\frac{?}{E}$ ratio $0\mathrm{.}25($i$.$e$.,$ to fund assets, the firm uses $$1$ from debt for every $$4$ from equity$),$ has outstanding bonds with a coupon rate of $10\%$ that sell at par and a beta equal to $1.$ The risk$-$free rate is $5\%$ and the expected market return is $15\%.$ The corporate tax rate is $30\%.$

Estimate the firm's weighted$-$average cost of capital $($WACC$).$

WACC