Answer:
The correct answer is OB.
Step-by-step explanation:
Let us recall the Associative Property of Addition: given three real numbers [tex]a[/tex], [tex]b[/tex] and [tex]c[/tex] the following equality holds:
[tex] (a+b) + c = a+(b+c)[/tex].
Let us remark that the Associative Property of Addition tells us that we can perform the sums in any order. So,
[tex] (n+2)+7 = n+(2+7)[/tex].
In the other options there was used the Commutative Property of Addition.