The graph below illustrates 2 intersecting lines. If a new line is drawn so that it passes through the red line at y = 0 and the blue line at x = –1, what is the slope of the new line?

To use the slope formula, we need to find two points. In this case, the points will be the point on the red line where y = 0 and the point on the blue line where x = -1. So, let's find those points completely so that we can properly use the slope formula.
Let's find the x-value of the coordinate on the red line where y = 0. To do this, let's find where the red line crosses y = 0 and find the x-value associated with it. You can see that the red line reaches y = 0 (the x-axis) at x = -4. So, one of our points is (-4, 0).
The next point is where the blue line crosses x = -1. To find the y-value associated with the coordinate of x = -1, let's find where the blue line is at x = -1 and see the y-value of the blue line at that point. By the graph, you can see that whenever the blue line is at x = -1, its value is -2. Thus, another coordinate point is (-1, -2).
Now that we have two points, we can use our slope formula. The slope formula is
[tex]m = \dfrac{y_2 - y_1}{x_2 - x_1}[/tex],
where [tex](x_1, y_1)[/tex] and [tex](x_2, y_2)[/tex] are points on the line that you are trying to find.
Let's "plug in" our values for the slope formula:
[tex]m = \dfrac{-2 - 0}{-1 - (-4)} = \dfrac{-2}{3} = - \dfrac{2}{3}[/tex]
We can see that the slope of the line would be -2/3.