A part has a design strength that is triangular, having the PDF fyly$]$ where $b$ is a constant equal to the maximum strength and $f(y)=3\frac{y}{b^3}0tb,0$ elsewhere.

$($a$)$ If the stress placed on the part is a constant b$/2.$ what is the static reliability? $($b$)$ If the above stress is applied at fixed intervals of $20$ duys to a tandomily selected part, what is days$)?($c$)$ if the above stress is applied randomly at a Poisson mean rate of once eveny $20$ days $10$ a part selected at random, what is days$)?[$B$]$