The equation is a linear one, therefore its graph will be a line on the plane.
To completely define a line we need two points.
We can use the information about the y-intercept and use it as one of the points we need. (0, -3)
As for the second point, we can get the x-intercept by setting y=0 and evaluating the function for x:
Then, we have the points we need: (0, -3) and (6,0).
Now, we only need to mark those points on the plane and draw a line through both of them.
Since the plane in the image only reaches the point (5,0), we need to calculate another point to specifically draw the graph on that grid.
Let set y=-1, then:
Now, we will use the points (0,-3) and (4,-1)