A pizza buffet has prepared 18 pizzas to place on the line at the beginning of lunch at 11:00 a.M. The equation y 14x + 18 can be used to describe the total number of pizzas that have been placed out on the buffet line, where x represents every 9 minutes after 11:00 a.M. Which statement best describes the rate of change in the number of pizzas set out on the buffet?