Answer: 
Associative and commutative properties of addition
Explanation: 
The one thing that the associative property of addition says that 

and the commutative property of addition says 

(the order of addition does not matter )
Now, the steps we take to solve our equation are the following: 

The second step is 

which simplifies to 

Hence, we used associative and commutative properties of addition to solve our equation.