In $2010$ Casey made a taxable gift of $$5\mathrm{.}7$ million to both Stephanie and Linda $($a total of $$11\mathrm{.}4$ million in taxable gifts$).$

Calculate the amount of gift tax due this year and Casey's unused applicable credit under the following alternatives. $($Refer to Exhibit $25-1$ and Exhibit $25-2.)$

b$.$ This year Casey made a taxable gift of $$15\mathrm{.}7$ million to Stephanie. Casey is not married, and the $2010$ gift was the only other taxable gift he has ever made.

c$.$This year Casey made a gift worth $$15\mathrm{.}7$ million to Stephanie. Casey married Helen last year, and they live in a common$-$law state. The $2010$ gift was the only other taxable gift Casey or Helen has ever made. Casey and Helen elect to gift$-$split this year.

Casey's gift tax due $$0$

Casey's unused applicable credit : $?$

Helen's gift tax due $$0$

Helen's unused applicable credit : $?$

PLEASE ANSWER BOTH PARTS