Serendipity Inc. is re$-$evaluating its debt level. Its current capital structure consists of $80\%$ debt and $20\%$ common stock, its beta is $1\mathrm{.}60$ and its tax rate is $25\%.$ However, the CFO thinks the company has too much debt, and he is considering moving to a capital structure with $40\%$ debt and $60\%$ equity. The risk$-$free rate $($RF$)$ is $5\mathrm{.}0\%$ and the market risk premium $($RP$.)$ is $7\mathrm{.}0\%.$ By how much would the capital structure shift change the firm's cost of equity $($r$.)?-5\mathrm{.}20\%$b$.-5\mathrm{.}78\%-6\mathrm{.}74\%-7\mathrm{.}00\%$