Suppose that lead$-$time demand is normally distributed with a mean of $250$ units and a standard deviation of $50$ units. If a firm wants to maintain a $95\%$ service level, what should the safety stock?

Group of answer choices

$82\mathrm{.}5$

$64\mathrm{.}0$

$332\mathrm{.}5$

$102\mathrm{.}5$