SAT Question 9d9fe1e6: Linear Functions answer and explanation with Desmos solution

Choice A is correct. It’s given that the function $f(x)=39-0.18x$ gives the estimated height, in centimeters (cm), of the fluid in the beaker $x$ days after the start of the experiment. For a function defined by an equation of the form $f(x)=b+mx$, where $m$ and $b$ are constants, $b$ represents the value of $f(x)$ when $x=0$. It follows that in the given function, $39$ represents the value of $f(x)$ when $x=0$. Since $x=0$ represents the start of the experiment, then the best interpretation of $39$ in this context is that the estimated height, in cm, of the fluid was $39$ at the start of the experiment.