SAT Question c8e0f511: Linear Equations In Two Variables answer and explanation with Desmos solution

Choice A is correct. It's given that for a camping trip a group bought $x$ one-liter bottles of water and $y$ three-liter bottles of water. Since the group bought $x$ one-liter bottles of water, the total number of liters bought from $x$ one-liter bottles of water is represented as $1x$, or $x$. Since the group bought $y$ three-liter bottles of water, the total number of liters bought from $y$ three-liter bottles of water is represented as $3y$. It's given that the group bought a total of $240$ liters; thus, the equation $x+3y=240$ represents this situation.