Allen, Co$.$ has $4,0007\%$ semiannual bonds outstanding. The bonds have $20$ years to maturity and sell for $103\%$ of par. Assume the company$$s tax rate is $35\%.$ What is the company$$s after$-$tax cost of debt?

$3\mathrm{.}37\%$

$6\mathrm{.}80\%$

$5\mathrm{.}37\%$

$7\mathrm{.}00\%$

$4\mathrm{.}37\%$

Show work please!