Final answer:
The constant of proportionality in the given proportional relationship is 0.45.
Step-by-step explanation:
A proportional relationship is one where the values of two variables are directly related to each other. In this case, we have x and y as the variables. To find the constant of proportionality, we can choose any two sets of corresponding x and y values and calculate the ratio between them. Let's choose the values (2, 9) and (4, 1.8) and calculate the ratio:
Ratio = y2/x2 = 1.8/4 = 0.45
The ratio is the same for all pairs of corresponding x and y values. Therefore, the constant of proportionality is 0.45.