Proportional relationship equation:
It is obvious that (0, 0) is one of the points regardless the value of k.
The graph of the proportional relationship is a line. To plot the line we need two points. One of them is the origin and the second point is based on the given details.
We would have the independent variable on the x-axis and the dependent variable on the y-axis.
In our case, independent variable is weight and dependent variable is cost.
The line for the first bag will have two points:
And for the second bag:
Plot the two points and connect to graph the lines.