WACC Olsen Outfitters Inc. believes that its optimal capital structure consists of $55\%$ common equity and $45\%$ debt, and its tax rate is $40\%.$ Olsen must raise additional capital to $2.$ fund its upcoming expansion. The firm will have $$4$ million of retained earnings with a cost of $r_s=11\%.$ New common stock in an amount up to $$8$ million would have a cost of $r_c=12\mathrm{.}5\%.$ Furthermore, Olsen can raise up to $$4$ million of debt at an interest rate of $r_d=9\%$ and an additional $$5$ million of debt at $r_d=13\%.$ The CFO estimates that a proposed expansion would require an investment of $$8\mathrm{.}2$ million. What is the WACC for the last dollar raised to complete the expansion?