5) $n^2 - 10n + 9$

We need two numbers that multiply to $9$ and add up to $-10$. The numbers are $-1$ and $-9$ since $(-1)\times(-9) = 9$ and $(-1)+(-9)=-10$.

Using the numbers from Step 1, we can factor $n^{2}-10n + 9$ as $(n - 1)(n - 9)$.

$(n - 1)(n - 9)$