k is the slope of the line formed by connecting the points.
Use slope formula:
\(\frac{y_2 - y_1}{x_2 - x_1}\)
where the 2 points are the end points of the line (First and last going Left to right)
\((x_1,y_1) = (2,7) \\ (x_2,y_2) = (8,28)\)
Substitute into slope formula
\(k= \frac{28-7}{8-2} = \frac{21}{6} = \frac{7}{2}\)
You can check if this is correct by going back to graph and going "up 7" and "over 2" to get from one point to the next.
