If Skye continues to use the same market$-$value capital structure, what is the firm's WACC assuming that $(1)$ it uses only retained earnings for equity and $(2)$ if it expands so rapidly that it must issue new common stock? $($Hint: Use the market value capital structure excluding current liabilities to determine the weights. Also, use the simple average of the required values obtained under the two methods in calculating WACC.$)$