Weekly demand for a VR Headset retailer has a mean of $20$ units. The supplier has a lead time of $15$ weeks. The cost of placing an order to the supplier each time is $$40,$ and annual holding cost for one unit is $20$ percent of the Cost of Goods. Each headset costs the retailer $$1,040.$ Assume $52$ weeks in a year.

Assume there is a weekly standard deviation in demand of $5$ units $($Chapter $11).$

If we have on average $25$ units of on$-$hand inventory, what is our stock$-$out probability?