The inside diameter decreases at an average rate of $\mathrm{.}001$ cm per part, and the process has a standard deviation of $\mathrm{.}05$ cm$.$ The variability is approximately normal. Assuming a three$-$sigma buffer at each end, how frequently must the tool be replaced if the process specifications are $3$ cm and $3\mathrm{.}5$ cm$.$ Use $($Number of shafts$)$ n $=1.$