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R$1=0\mathrm{.}94$

R$2=0\mathrm{.}89$

R$3=0\mathrm{.}64$

R$4=0\mathrm{.}76$

Xiaohei designed the system above with her engineering team.

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

$($b$)$ If they have to pay $$$$3$ comma $700$ to fix a failed$$ system, what is the expected failure cost of the$$ system? $$$$\_\_\_\_\_($round your response to the nearest $$dollar$).$

$$

$($c$)$ If Xiaohei installs R$5$ as a backup for R$4.$ R$5$ has a reliability of $95\%.$ The probability of failure of the system with R$5$ is $\_\_\_\_$ enter your response as a percentage rounded to two decimal$$ places$).$

$($d$)$ How much should they pay for R$5$ at the$$ maximum? $$$$\_\_\_\_\_$

$($round your response to the nearest $$dollar$).$