SAT Question 0eae6be1: Linear Functions answer and explanation with Desmos solution

Choice D is correct. It's given that the number $y$ is $84$ less than the number $x$. A number that's $84$ less than the number $x$ is equivalent to $84$ subtracted from the number $x$, or $x-84$. Therefore, the equation $y=x-84$ represents the relationship between $x$ and $y$.