The graph shows the amount of money paid when purchasing bags of peanuts at the zoo: a graph is shown. the x-axis is labeled from 0 to 9. the y-axis is labeled from 0 to 13. the four points shown on the graph are ordered pairs 0, 0 and 1, 4 and 2, 8 and 3, 12. these points are joined by a line. the label on the x-axis is bags of peanuts. the title on the y-axis is total cost in dollars. write an equation to represent the relationship between the total cost (y) and the number of bags of peanuts (x).