You were hired as a consultant to Giambono Company, whose target capital structure is $55\%$ debt, $15\%$ preferred, and $30\%$ common equity. The after$-$tax cost of debt is $6\mathrm{.}00\%,$ the cost of preferred is $8\mathrm{.}50\%,$ and the cost of retained earnings is $15\mathrm{.}75\%.$ The firm will not be issuing any new stock. What is its WACC?

a$.9\mathrm{.}30\%$

b$.6\mathrm{.}00\%$

c$.8\mathrm{.}03\%$

d$.4\mathrm{.}58\%$

e$.10\mathrm{.}08\%$