Okay. If we were writing this in y=mx+b, we know that m is the slope and b is the y-intercept.
On the graph, we can see that the line crosses the -2 on the y-axis. So, -2 is the y-intercept(b).
The rise over run is 8 down/up and 8 across.
So your answer should be y=-1x-2. Since the line is going down, the slope is negative.
Hope this helps!