In the college parking lot, each employer is allotted $40$ free hours of parking per week. After that, they pay $5$ dollars per hour up to $50$ hours, $8$ dollars per hour from $50$ hours to $60$ hours, and $15$ dollars for each hour after that. An employer received a parking bill of $82$ dollars for the week. How many hours did he park his car in the parking lot? 
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