3) Simplify the expression \( \frac{2a + 18}{a^2 + 18a + 81} \).

\( \frac{2a + 18}{a^2 + 18a + 81} = \frac{2(a + 9)}{(a + 9)^2} = \frac{2}{a + 9} \) (assuming \( a \neq -9 \)).