B$.$F$.$ Pierce & Company is considering changing its capital structure. The company currently has no debt and no preferred stock, but it would like to add some debt to take advantage of low interest rates and the tax shield. Its investment banker has indicated that the pre$-$tax cost of debt under various possible capital structures would be as follows:

$\backslash$table$[[\backslash$table$[[$Market Debt$-$to$-],[$Value Ratio$]],\backslash$table$[[$Market Equity$-$to$-],[$Value Ratio$]],\backslash$table$[[$Market Debt$-$to$-],[$Equity Ratio$]],\backslash$table$[[$Before$-$Tax Cost of$],[(w_D)$