SAT Question c1bd5301: Linear Functions answer and explanation with Desmos solution

For a certain animal, it's given that a model predicts the animal weighed $241$ pounds when it was born and gained $3$ pounds per day in its first year of life. It's also given that this model is defined by an equation in the form $f\left(x\right)=a+bx$, where $f\left(x\right)$ is the predicted weight, in pounds, of the animal $x$ days after it was born, and $a$ and $b$ are constants. It follows that $a$ represents the predicted weight, in pounds, of the animal when it was born and $b$ represents the predicted rate of weight gain, in pounds per day, in its first year of life. Thus, the value of $a$ is $241$.