Considering a system with its Reliability Block Diagram $($RBD$)$ illustrated below and assuming every component works independently. The reliabilities of components $1$ and $5$ are given as R$1=$ R$5=0\mathrm{.}9,$ the reliabilities of components $2,3,$ and $4$ are given as R$2=$ R$3=$ R$3=0\mathrm{.}8,$ and the reliabilities of components $6,7,$ and $8$ are given as Ro $=$ R$,=$ Rg $=0\mathrm{.}7.$ As shown in the RBD$,$ components $6,7,$ and $8$ works in the $2$ out of $3$ redundancy mode. $==6231572/348($a$)$ Calculate the reliability of the entire system. $(10$ marks$)($b$)$