Which number sentence shows the associative property of addition? choose all that apply. 3z + 9p = 9p + 3z 3x(5 + 2) = 3x(5) + 3x(2) 3 + (2 + 8) = (3 + 2) + 8 (6 + 1) + 9 = 6 + (1 + 9)