Answer:
[tex]-\dfrac{2}{3}[/tex]
Step-by-step explanation:
When variable y is said to be proportional to another variable x, it is written as:
[tex]y \propto x[/tex]
To introduce the equality sign, we introduce what is called the constant of proportionality, say k and write the above as:
y=kx
Comparing the given equation:
[tex]y=-\frac{2}{3}x[/tex]
We can see that our constant of proportionality:
[tex]k=-\dfrac{2}{3}[/tex]