Answer
$(3+7)+9 = \underline{3} +(7+\underline{9})$
Work Step by Step
The associative property states that for any real numbers a, b, and c:
$a + (b+c) = (a+b)+c$
Thus, apply the associative property to the given problem to find:
$(3+7)+9 = 3 +(7+9)$
