Final answer:
The addition property being illustrated is the Associative Property of Addition, which states that the grouping of numbers does not affect the sum.
Step-by-step explanation:
The addition property being illustrated in the given equation is the Associative Property of Addition.
The Associative Property states that when adding three or more numbers, the grouping of the numbers does not affect the sum. This means that you can rearrange the parentheses and still get the same result.
In the given equation, both sides of the equation are equal: (6 + 7) + 1 = 6 + (7 + 1). This demonstrates the Associative Property of Addition.