A movie theater charges $8.50 for an adult ticket to an evening showing of a popular movie. To help the local animal shelter, the theater management has agreed to reduce the price of each adult ticket by $0.50 for every can of pet food a customer contributes to a collection barrel in the theater lobby. Which of the following shows both an equation in which y represents the cost of an adult ticket in dollars for a customer who contributes x cans of pet food, and the graph of the cost if a customer brings in 2, 5, 8, or 10 cans of pet food?