Final answer:
The function rule that models the situation is y = 20 + 12x, where y represents the total cost and x represents the number of hours. The constant term of $20 represents the fixed charge and the coefficient of 12 represents the hourly rate.
Step-by-step explanation:
The given situation involves a lawn service that charges $20 plus $12 per hour to mow and edge a yard. In order to write a function rule that models this situation, we can define the total cost as a function of the number of hours spent working. Let's call the total cost y and the number of hours x. The function rule can be represented as:
y = 20 + 12x
In this function rule, the constant term of $20 represents the fixed charge for the lawn service, and the coefficient of 12 represents the hourly rate. By substituting different values for x (the number of hours), we can determine the total cost for different amounts of work.