An equation has a constant of proportionality if x is a multiple of y or vice-versa.
We simplify each equation
A) [tex]4y=4x \\ y=x[/tex]
B) [tex]4y=12x \\ y=3x[/tex]
C) [tex]3y=4x \\ y= \frac{4}{3}x [/tex]
D)[tex]3y=12x \\ y=4x[/tex]
Only D has constant of proportionality equal to 4 so D is the answer
