Slope = (y2 - y1)/(x2 - x1)
y2 represents the final value of y on the vertical axis
y1 represents the initial value of y on the vertical axis
x2 represents the final value of x on the horizontal axis
x1 represents the final value of x on the horizontal axis
From the graph,
x1 = - 3, x2 = 3
y1 = 4, y2 = 2
Slope = (2 - 4)/(3 - - 3
Slope = - 2/6
Slope = - 1/3