Firm A plans to issue a $$1,000$ par value, $20-$year noncallable bond with a $7\mathrm{.}00\%$ annual coupon, paid semiannually. The firm is considering a change in the corporate tax rate to $30\mathrm{.}00\%.$ By how much would the after$-$tax cost of debt $($i$.$e$.,$ r$\_$d $\backslash$times $(1-$T$))$ using the new tax rate decrease?$1\mathrm{.}0\mathrm{.}77\%2\mathrm{.}0\mathrm{.}85\%3\mathrm{.}0\mathrm{.}70\%4\mathrm{.}0\mathrm{.}63\%5\mathrm{.}0\mathrm{.}57\%$