$($a$)$ A pressure vessel has an internal diameter $16$ in and outer diameter $18$ in$.$ Is it a thin or thick wall pressure vessel?$(3$ points$)$

$($b$)$ Consider the cylinder is subjected to an internal pressure of $100$ psi. Assume the cylinder is capped.

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Find the Maximum shear stresses at diameter $16\mathrm{.}25$ in$.(7$ points$)$