Answer: D) Commutative property of addition
Explanation:
When going from the "given" to "step 1", we swap the positions of -20 and 3x. We use the commutative property of addition to get this done. That general rule is x+y = y+x. We can add in any order.
An example of this is 8+9 = 9+8 both sides lead to 17. Note that subtraction is the same as adding a negative. So we can think of 3x-20 as 3x+(-20).
