If the ordered pairs are coordinates of points, divide the abscissas by the ordinates to get the constant of proportionality (r) x/y.
a. (2, 3) r = 2/3
b (3, 4.5) r = 3/4.5 = 2/3
c. (4, 6) r = 4/6 = 2/3
d. (5, 7.5) r = 5/7.5 = 2/3
Thus, the answer is 2/3 for all the ordered pairs.