Since you have the slope m = -3 and the point (-9, -2) you can use the Slope Intercept Form to find b
y = mx + b
-2 = -3(-9) + b
-2 = 27 + b
Subtract 27 from both sides of the equation to get b
-2 - 27 = b
-29 =b
And the Slope Intercept Form
y = -3x -29
Now you can rearrange the Slope Intercept Form to give the Standard Form by adding 3x to both sides of the equation.
y + 3x = -29
I hope you find this useful and if you have any questions please send me a message.