We would first need to make the equation in slope intercept form: y=mx+b
y+9=-3x
Subtract 9 to both sides:
y=-3x-9
So the slope is -3 and the y intercept is -9.
Plot a point at y=-9, or -9 on the y-axis. Then, go down three and right one unit and plot a point, then repeat. Once you cannot plot anymore, switch to the left side of -9. Go up 3 and left one unit and plot a point, then repeat.