$5(20$ points$).$ The following table presents the demands for $3$ seasons $)=(3.$ The periodicity $0.$

$\backslash$table$[[$Period $t,-11,-10,-9,-8,-7,-6,-5,-4,-3,-2,-1,0],[$Demand $D_t,9,20,26,17,12,23,30,22,15,26,34,25]]$

$($a$)(5pts)$ Find $G_0.$

$($b$)(5pts)$ Find $S_0.$

$($c$)(5$ pts$)$ Compute the $($initial$)$ seasonal factor for period $t=-3.$

$($d$)(5$ pts$)$ If the $4$ final seasonal factors are $c_1=0\mathrm{.}59,c_2=1\mathrm{.}1,c_3=1\mathrm{.}38,$ and $c_4=0\mathrm{.}93,$ find forecast $F_3($for period $t=3).$