don't know what to do. What is the slope of the roof?

The slope of a line is given by the formula,
Slope = change in y over change in x.
Better still,
[tex]\begin{gathered} m=\frac{y_2-y_1}{x_2-x_1} \\ \text{This can also be written as,} \\ m=\frac{\Delta y}{\Delta x} \\ \text{Where }\Delta\text{ represents the change in the variables y and x} \\ m=\frac{17-8}{12} \\ m=\frac{9}{12} \\ m=\frac{3}{4} \\ OR \\ m=0.75 \end{gathered}[/tex]Please note that on the y axis, the change is from 8 to 17, while on the x axis, the change between both points has already been marked as 12