You would use the distributive property and addition to simplify this equation.
Let's start from left to right:
3-9= -6
Distribute -6 through to -2 and positive x:
-6(-2)= 12 (negatives cancel each other out and become positive)
-6(x)= -6x
New equation;
12-6x-9x
Now we would add together like the terms (x):
-6x+(-9x)= -15x
Don't forget that 12!
12-15x is your simplified answer.
Hope that helps explains!
