Final answer:
In Mathematics, specifically linear equations, the total cost of a phone plan (y) is being related to the minutes used (x) through a series of given options. Without additional context, the correct equation for the Ringular plan cannot be identified from the given options.
Step-by-step explanation:
The subject of the question is Mathematics, specifically related to forming an equation that relates two variables.
In the context provided, the Ringular plan seems to represent a phone service plan where the total monthly cost (y) depends on the monthly minutes used (x). The given options are different linear equations that combine a fixed cost with a variable cost per minute. From the information provided, such as 'the total cost is y = 31.50 + 32x', we can compare the structure to the options given in the question. Each equation represents a possible pricing model for phone plans, where there is typically a base fee plus a charge per minute of use.
It's important to note that without more context or specific details about the Ringular plan's pricing model from the problem statement, it's not possible to determine which option (A, B, C, or D) is correct. Additional information, such as the fixed monthly fee or the cost per minute, would be needed to accurately identify the equation for the Ringular plan.