please help
A consulting firm conducts training sessions for employees of various companies. The charge to a company sending employees to a session is $50 per employee, less $0.50 for each employee in excess of 10. That is, for example, if twelve employees are sent, the charge per employee would be $49.00 and the total prorated charge to the company would be 12(49.00)=$558.00. The consulting firm further has a fixed total charge for groups of x or more where x is the number that maximizes the prorated group charge. What should x be, and what is the maximum total group charge to the company?

Question

please help 
A consulting firm conducts training sessions for employees of various companies. The charge to a company sending employees to a session is $50 per employee, less $0.50 for each employee in excess of 10. That is, for example, if twelve employees are sent, the charge per employee would be $49.00 and the total prorated charge to the company would be 12(49.00)=$558.00. The consulting firm further has a fixed total charge for groups of x or more where x is the number that maximizes the prorated group charge. What should x be, and what is the maximum total group charge to the company?