That would be elimination. you could do it with substitution but i like using elimination more than substitution when theres more than 2 variables
Answer:
A..., 1, 1/2", 1/4", 1/8"...
Step-by-step explanation:
Your answer would be 11a-6 because when you subtract 12a-9a you get 3a and the you add 8a-6 it would equal 11a-6
