Answer is -1/3
Pick a point on your line and use rise over run to help. For example, take the coordinates (6,7), you are going to rise 1 and move over 3 until you hit the next coordinate on your line. You can either do this before or after you found your slope, but you need to determine if your graph is positive or negative. If your graph is positive it will be going up, but if it’s going down like in your picture then it’s negative.
Hope this helps:)