A telecom service provider engages male and female operators for answering $1000$ calls per day. A male operator can handle $40$ calls per day whereas a female operator can handle $50$ calls per day. The male and female operator get a fixed wage of Rs. $250$ and Rs. $300$ per day respectively. In addition, a male operator gets Rs. $15$ per call he answers and a female operator gets Rs. $10$ per call she answers. To minimize the cost how many male operators should the service provider employ assuming he has to employ more than $7$ of the $12$ female operators available for the job?