Olsen Outfitters Inc. believes that its optimal capital structure consists of $60\%$ common equity and $40\%$ debt, and its tax rate is $25\%.$ Olsen must raise additional capital to fund its upcoming expansion. The firm will have $$4$ million of retained earnings with a cost of rs $=13\%.$ New common stock in an amount up to $$8$ million would have a cost of re $=14\mathrm{.}5\%.$

Furthermore, Olsen can raise up to $$4$ million of debt at an interest rate of rd $=11\%$ and an additional $$4$ million of debt at rd $=13\%.$ The CFO estimates that a proposed expansion would require an investment of $$8\mathrm{.}6$ million.

What is the WACC for the last dollar raised to complete the expansion?