A $9\mathrm{.}1\%$ coupon bond issued by the state of Indiana sells for $$1,000.$ What coupon rate on a corporate bond selling at its $$1,000$ par value would produce the same after$-$tax return to the investor as the municipal bond if the investor is in the $15\%$ marginal tax bracket?

$10\mathrm{.}7\%$

$8\mathrm{.}1\%$

$9\mathrm{.}5\%$

$11\mathrm{.}6\%$