The total cost is the IP's fixed monthly charge, plus the IP's total access fee. The IP's total access fee is the product of the IP's per-logon fee and the number of user logons.

The profit is the difference between the income and the outgo. The income is the product of the number of users and the per-user fee that you charge. The total outgo is the cost you figured above.

Take the derivative of your profit function, and find the max point.

If you get stuck, please reply showing your work and reasoning so far, starting with the algebra for the first two parts.

Thank you!