Final answer:
The property demonstrated by the statement is the associative property of addition.
Step-by-step explanation:
The property demonstrated by the statement 5+(8+g)=(5+8)+g is the associative property of addition.
The associative property of addition states that when adding three or more numbers, the grouping of the numbers does not affect the sum. In other words, you can add the numbers in any order and still get the same result.
For example, in the given statement, you can add 8+g first and then add 5 to the result, or you can add 5+8 first and then add g to the result. In both cases, the sum will be the same.