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ABC Inc's semi$-$annual bonds have a price of $$720,$ an $9\mathrm{.}90\%$ coupon rate and mature in $12$ years. The company's tax rate is $41\%.$ What is its after$-$tax cost of debt when calculating its WACC?

a$.$

$8\mathrm{.}85\%$

b$.$

$4\mathrm{.}42\%$

c$.$

$15\mathrm{.}00\%$

d$.$

$9\mathrm{.}90\%$

e$.$

$5\mathrm{.}84\%$