Upper R $2$R$2$equals$=0\mathrm{.}840\mathrm{.}84$

Upper R $1$R$1=0\mathrm{.}920\mathrm{.}92$

Upper R $4$R$4$equals$=0\mathrm{.}750\mathrm{.}75$

Upper R $3$R$3$equals$=0\mathrm{.}680\mathrm{.}68$

Xiaohei designed the system above with her engineering team.

$($a$)$ The overall system reliability is enter your response here$\%($enter your response as a percentage rounded to two decimal $$places$).$

$($b$)$ If they have to pay $$$$3$ comma $4003,400$ to fix a failed$$ system, what is the expected failure cost of the$$ system? $$$enter your response here $($round your response to the nearest $$dollar$).$

$($c$)$ If Xiaohei installs R$5$ as a backup for R$4.$ R$5$ has a reliability of$8585\%.$ The probability of failure of the system with R$5$ is enter your response here$\%($enter your response as a percentage rounded to two decimal$$ places$).$

$($d$)$ How much should they pay for R$5$ at the$$ maximum? $$$enter your response here $($round your response to the nearest $$dollar$).$