Show your work: this question.

Clara 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 $$4,200$ to fix a failed system, what is the expected failure cost of the system? $ $($round your response to the nearest dollar$).$

$($c$)$ If Clara wants to add $a(n)85\%-$reliable backup to R$4,$ how much should they pay for the backup at the maximum? $ $($round your response to the nearest dollar$).$