production and operations analytics $8$ edition section $9\mathrm{.}4$ problem $14$

a single inventory item is ordered from an outside supplier. the anticipated demand for this item over the next $12$ months is $6,12,4,8,15,25,20,5,10,20,5,12.$ current inventory is $4,$ and ending inventory should be $8.$ assume a holding cost of $$1$ per period and a setup cost of $$40.$ What are the steps to determine the $$least unit cost$$