To determine the slope of a graphed line you have to use the following formula:
Where
(x₁,y₁) are the coordinates of one point on the line
(x₂,y₂) are the coordinates of another point of the line
So the first step is to identify two points of the line, for example, the points (2,6) and (0,-2)
You can use (x₁,y₁) → (2,6) and (x₂,y₂) → (0,-2), replace the coordinates on the formula:
The slope of the line is m=4