12. Carly's family is going to buy cell phones for the entire family. After some research they have narrowed their choices
down to 2 companies. AT&T charges a monthly rate of $100 plus $15 for each phone on the account. Their competitor,
Sprint, charges a flat monthly fee of $200 and they will receive an unlimited number of phones on the account.
a. Write an equation for the cost of each cell phone provider and then graph the equations.
AT&T:
Sprint:
b. Use any method to determine which company would be cheaper if Carly's family consists of Carly, mom, dad, two brothers, and one sister. Explain your reasoning