$($a$)$ A subassembly of a mobile system consists of $3$ different components $K,P$ and $S.$

Because of low reliability Component $K$ has been replicated and $6$ of $K$ have been

used. Reliabilities per $830$ hours of $K=0\mathrm{.}65$ and $P=0\mathrm{.}90$ and $S=0\mathrm{.}94$

i$)$Find the system failure rate per $415$ hours and MTBF

ii$)$ System reliability per $750$ hours.