Paisley Choi's Biogas Solutions has outstanding semiannual coupon bonds with a face value of $$1,000,$ a $10\%$ coupon rate, $25$ years remaining until maturity, and a current market value of $$842\mathrm{.}38.$ If the company$$s tax rate is $25\%,$ what is the after$-$tax cost of debt?

a$.$

$0\mathrm{.}05$

b$.$

$0\mathrm{.}09$

c$.$

$0\mathrm{.}06$

d$.$

$0\mathrm{.}12$