Which property of equality is x + (3x + 20) = 180?

Question

I am looking to find the answer to these problems - Which property of equality are each of these? The options I have are distributive, addition, subtraction, multiplication, division, transitive, symmetric, substitution, and reflexive.

 

1. x + (3x + 20) = 180

2. 4x + 20 = 180

3. x = 40

 

Thank you :)

Answer 1

In solving for x, you used the associative property in this step:

 

x + (3x + 20) = (x + 3x) + 20