Solving proportions with $3$ ratios,$ x:3:y = -2:3:-4$ Proportion seems simple enough for me. Example is $4:x = 2:5,$ and the answer is $x = 10.$
My problem is how do I solve for proportions with $3$ ratios like $x:3:y = -2:3:-4$ ?
Do I write it like
$$\frac{\frac{x}{3}}{y} = \frac{\frac{-2}{3}}{-4} $$
?

Just like chained equalities, you can break it apart.  $x:3:y=-2:3:-4$ becomes $x:3=-2:3$ and $3:y=3:-4$.  Now solve them independently.
