Twenty$-$five samples of size $4$ resulted in statistics of

$$

$$

$$

$=$

$38\mathrm{.}0$

minutes and

$$

$$

$=$

$3\mathrm{.}0$

minutes for the Turkmaster Cleaning Company$$s average time to completely clean a rug. Compute control limits for

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$$

$-$ and R$-$charts and estimate the standard deviation of the process.