Commutative property means that you can rewrite the equation in a different order. So for example, if I have 3 + 8 + 5 I can rewrite it as 5 + 3 + 8 or 8 + 5 + 3 and so on and so forth. So, we must go over all the options to narrow it down. It isn't B or C, So lets look at D. D shows you 12 + 6 + 15 = 12 + 6 + 15 this is the wrong answer because it does not rewrite the equation. It just repeats itself so lets take a look at option A. A says 12 + 6 + 15 = 12 + 15 + 6 this is the correct answer because it rewrote the equation in a different order but they are still the same numbers.
So the correct answer is
A) 12 + 6 + 15 = 12 + 15 + 6