Answer:
k=3
Step-by-step explanation:
we know that
A relationship between two variables, x, and y, represent a proportional variation if it can be expressed in the form [tex]k=\frac{y}{x}[/tex] or [tex]y=kx[/tex]
In this problem we have
[tex]y=3x[/tex]
therefore
The constant of proportionality is k=3
