From $2008$ to $2012,$ the total numbers of births B $($in thousands $)$ an B$($t$)=4\mathrm{.}917$t$^(3)-124\mathrm{.}71$t$^(2)+925\mathrm{.}9$t$+2308$ and D$($t$)=-7\mathrm{.}083$t$^(3)+222\mathrm{.}64$t$^(2)-2281\mathrm{.}8$t$+10,104$ where t represents the year, with t$=8$ corresponding to $2008.$ Find B$($t$)-$D$($t$)$