The phone company Splint has a monthly cellular plan where a customer pays a flat monthly fee and then a certain amount of money per minute used on the phone. If a customer uses 400 minutes, the monthly cost will be $131. If the customer uses 760 minutes, the monthly cost will be $221.

A) Find an equation in the form $\displaystyle {y}={m}{x}+{b},$ where $\displaystyle {x}$ is the number of monthly minutes used and $\displaystyle {y}$ is the total monthly of the Splint plan.

Answer: $\displaystyle {y}=$
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Do no use any commas in your answer.

B) Use your equation to find the total monthly cost if 688 minutes are used.

Answer: If 688 minutes are used, the total cost will be dollars.