For a function $f$, $f(1)=8$ and $f(-2)=-4$. If the graph of $y=f(x)$ is a line in the $xy$-plane, what is the slope of the line?

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We can convert the given information into $(x,y)$ coordinates.

$$f(1)=8;   (1,8)$$ $$f(-2)=-4;   (-2,-4)$$

Using the slope equation,

$$m=\frac{y_2-y_1}{x_2-x_1}$$ $$m=\frac{8-(-4)}{1-(-2)}$$ $$m= \frac{12}{3}$$ $$m=\boxed{4}$$