The buyer for Department Store A$,$ a famous $$high$-$end$$ department store, must decide on the quantity of a high$-$priced backpacks to procure for the following Christmas season.

The unit cost of the backpacks to the store is $$28\mathrm{.}50$ and each handbag will sell for $$150\mathrm{.}00.$ Any backpacks not sold by the end of the season are purchased by a discount firm for $$10\mathrm{.}00.$ And there is no penalty for loss of customer goodwill.

Suppose the buyer has determined the underage cost and overage cost to be cu$=$ $$100$ per unit and co$=$ $$10$ per unit, respectively. Then the desired customer service level is $\_\_\_\_\_\_?$ Round to three decimal places.