The specification for the diameters of ball bearings is $15\mathrm{.}40-15\mathrm{.}60mm.$ Data from an $\stackrel{}{x}$ chart, based on samples of size $8,$ that shows that the process is in control, yield values of $\frac{?}{\text{b}\text{a}\text{r}}(\stackrel{}{x})=15\mathrm{.}52$ and $\frac{?}{\text{b}\text{a}\text{r}}(R)=0\mathrm{.}05.$

a$.$ Compute the value of $C_{pk}$ for this process.

b$.$ Is the process capability acceptable? Explain.