$20.$ What is the Cpk value after improvement for Exercise $18$ when the process center is $6\mathrm{.}40?$ When the process center is $6\mathrm{.}30?$ Explain$\mathrm{.}18.$ Determine the capability index before $($s$0=0\mathrm{.}038)$ and after $($s$0=0\mathrm{.}030)$ improvement of Example Problem $5-8$ using specifications of $6\mathrm{.}40\{0\mathrm{.}15$ mm$.$