Company Y has a target debt to equity ratio of $50\%.$ Currently its book debt to equity ratio is $60\%$ and it expects to revert to the target ratio very soon. The company has an after$-$tax market cost of debt of $9\%$ and a market cost of equity of $20\%.$ What is the WACC for the company?

a$.$

$16\mathrm{.}51\%$

b$.$

$14\mathrm{.}33\%$

c$.$

$13\mathrm{.}50\%$

d$.$

$12\mathrm{.}33\%$