Final answer:
The Commutative Property of Addition states that the order of the numbers can be changed without affecting the result.
Step-by-step explanation:
The property being used here is the Commutative Property of Addition, which states that the order of the numbers can be changed without affecting the result.
In the given example, 4 + 5 and 5 + 4 both result in 9, showing that the order in which the numbers are added does not matter.
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