Your answer would be b i'm pretty sure
Start with

Expand both parentheses by multiplying both terms by the number outside:

Sum like terms:

Simplify the "+3" on both sides:

Subtract 2x from both sides:

Divide both sides by 2:

Answer:
The correct answer is the associative property of addition.
Step-by-step explanation:
This property states that no matter which way we group things when adding, they will still create the same outcome. Since all of the symbols are addition, the answer is the same.