Answer
18
Work Step by Step
$(n+9)^{2}$
Use FOIL to simplify. FOIL: First (Multiply the first variables in the brackets), outside (Multiply the outer variables), Inside (Multiply the inside variables), Last (Multiply the last variables in the brackets).
(n)(n) + 9(n) + 9(n) + (9)(9)
$n^{2}$ + 9n + 9n + 81
We add the 9n and 9n to get the simplified answer.
$n^{2}$ + 18n + 81
Thus the middle term is 18n and the number is 18.
