Suppose that Generic Retailer is undergoing a CRM $($customer relationship management$)$ review, and as part of this review, it is reconsidering its stocking policy for a certain electronic item. Annual sales of this item equal $40,000$ units. The cost of the item is $$190/$unit$,$ the units sell for $$199\mathrm{.}95$ each $($and are never on sale$),$ and the holding cost per unit per year is $25\%$ of its cost. Generic is open $365$ days a year.

The probability that the item is in stock at any given time is called the service level. Generic has some information about how changes in service levels will change gross sales. For service levels under $95\%,$ each $1\%$ change in service level $($up or down$)$ changes gross sales by $0\mathrm{.}25\%.$ But for service levels at or exceeding $95\%,$ each $1\%$ change will move gross sales by $0\mathrm{.}20\%.$ Right now Generic maintains a $91\%$ service level for this item.

When this item is ordered, it takes ten days for the order to be received. The demand over this $10$ day period is approximately normal. It averages approximately $1,096$ units $($check this!$),$ with a standard deviation over the $10$ days of $150$ units.

Find, to the nearest percent, the optimal service level for this product.