The phone company Splint has a monthly cellular plan where a customer pays a flat fee for unlimited voice calls and then a certain amount per GB of data used. If a customer uses 2 GB, the monthly cost will be $39. If the customer uses 22 GB, the monthly cost will be $129. A) Find an equation in the form y = m x + b , where x is the number of GB of data used in a month and y is the total monthly cost of the Splint plan. y =

B) Use your equation to find the total monthly cost if 12 GB are used. If 12 GB are used, the total cost will be dollars.