A basic cellular package costs $40/month for 60 minutes of calling with an additional charge of $0.20/minute beyond that time. The cost function C (2) for using z minutes would be If you used 60 minutes or less, i.e. if if x < 60, then C (z) = 40 (the base charge). If you used more than 60 minutes, i.e. (x-60) minutes more than the plan came with, you would pay an additional $0.20 for each of those (x-60) minutes. Your total bill would be C(z) = 40+0.20 (x-60). If you want to keep your bill at $50 or lower for the month, what is the maximum number of calling minutes you can use?