SAT Question 70a2776f: Two-variable Data Models And Scatterplots answer and explanation with Desmos solution

Choice A is correct. It's given that the data shown in the scatterplot give the recorded temperature, in degrees Celsius, for $7$ depths, in meters, below the surface of a lake. The graph of an appropriate line of best fit for the data shown passes approximately through the points $(15,21.8)$ and $(70,12.7)$. The slope of a line in the xy-plane that passes through the points $(x_1,y_1)$ and $(x_2,y_2)$ can be calculated as $\frac{y_2-y_1}{x_2-x_1}$. Substituting $(15,21.8)$ and $(70,12.7)$ for $(x_1,y_1)$ and $(x_2,y_2)$, respectively, in the expression $\frac{y_2-y_1}{x_2-x_1}$ yields $\frac{12.7-21.8}{70-15}$, or $\frac{-9.1}{55}$, which is approximately $-0.165$. Therefore, of the given choices, $-0.17$ is closest to the slope of a line of best fit for the data shown.