Answer:
y = -x -3
Step-by-step explanation:
The slope intercept form is
y = mx+b where m is the slope and b is the y intercept
3x+3y = -9
Subtract 3x from each side
3x-3x+3y = -3x-9
3y = -3x-9
Divide each side by 3
3y/3 = -3x/3 -9/3
