Answer:
r = 0.5
Explanation:
Since we're told that the quantities x and y are proportional and this is represented by the equation y = rx, one variable is a constant multiple of the other.
Thus, we can find r by simply plugging in one of the quantities for y and its corresponding x value and isolating r.
Let's use 9 for x and 4.5 for y:
(4.5 = 9r) / 9
0.5 = r
Thus, the constant of proportionality is 0.5.
This means that x is constantly multiplied by 0.5 to get y.