A company has a $\frac{D}{E}$ ratio of $80\%.$ Suppose its equity beta is $0\mathrm{.}5,$ and the market risk premium is $5\mathrm{.}4\%.$ Also suppose the risk$-$free rate is $1\mathrm{.}8\%,$ and the YTM on the company's debt is $2\mathrm{.}6\%.$ Find its WACC $($Assume a tax rate of $10\%.)$