a. In a proportional relationship, the equation that relates the variables (x and y) is:
y = kx
where k is some constant.
This relationship corresponds to the equation of a line that passes through the origin. The graph that relates weight and costs is the graph of a line that passes through the origin, then the relationship is proportional.
b. The point (5, 12.5) means that when x = 5, y = 12.5, that is, when the weight is 5 pounds, the price is $12.5
