A copy center processes $18$ orders per day, on average. Assume a $6$ hour day. Assume the center has more than enough machines to meet the demand. On average, one order takes $10$ minute to set up the machine and $20$ minutes to print, package and label the order. At the end of a working day, how many orders are still in process?

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At the end of a working day, how many orders are still in process?