Final answer:
The constant of proportionality is 1/5.
Step-by-step explanation:
To find the constant of proportionality, we need to use the given information that y varies directly with x and that y = 9 when x is 45.
The equation that represents this relationship is y = kx, where k is the constant of proportionality.
Substituting the values y = 9 and x = 45 into the equation, we can solve for k:
9 = k * 45
k = 9/45
k = 1/5
Therefore, the constant of proportionality is 1/5.