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 12 and the y-axis is labeled from 0 to 12. the four points are 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. what is the constant of proportionality?