The points we can clearly see are (-2,-2) and (0,-3). You have to rise up 2 points and got to the left 4, so the rise over run is 2 over -4. Simplify this to -1/2, so the slope is negative 1/2.
To know the slope of a line we can have the equation or to know points of the line. In this case from the graph we can get to points (-4,-1) and (0,-3). Having this and using the equation to calculate the slope, we have:
Defining:
and
Replacing this values in the initial equation, this is: