Answer:
y = 1x -5 
Explanation:
y = mx + b
Since the line crosses the y axis at -5, that is our y-intercept and the b of the equation. 
The slope is the rise over the run. Now the line goes down one and left one. This makes our slope 1/1 which we simply write as 1. 
So the equation is y = 1x -5.