In $2010$ Casey made a taxable gift of $$6\mathrm{.}8$ million to both Stephanie and Linda $($a total of $$13\mathrm{.}6$ million in taxable gifts$).$ Calculate the amount of gift tax due this year and Casey$$s unused exemption equivalent under the following alternatives. $($Refer to Exhibit $25-1$ and Exhibit $25-2.)$