Smylie & Son uses a fixed$-$period system $to$ manage its inventory $of$ hand$-$rolled cigars. One model, the $el$ diablo,$$ enjoys robust demand $at480$ boxes per week $(20$ cigars per box$)$ with a standard deviation $of120.$ Cigars must $be$ stored $in$ a carefully controlled climate, $so$ storage costs are $$\frac{5}{c}$igar per year. Smylie and Son$s$ supplier $is$ located $onan$ island south $of$ Miami, Florida, and ordering $is$ complicated and thus expensive, $at$ $$1,500an$ order. Even $at$ that price, $it$ takes $an$ average $of$ six weeks $to$ receive a shipment. $El$ diablo $is$ popular even $at$ the exorbitant price Smylie & Son charges, $so$ the company $is$ loath $to$ run out $of$ stock and has set its service level $at$ a respectable $99$ percent. What should the review period $be?$

$a.$

$8$ weeks

$b.$

$7$ weeks

$c.$

$6$ weeks

$d.$

$9$ weeks