To simplify \( \sqrt{54} \), we can factor 54 into its prime factors:
\[ 54 = 2 \times 3^3 \]
Now we can take out any square factors from the radical:
\[ \sqrt{54} = \sqrt{2 \times 3^3} = \sqrt{2} \times \sqrt{3^2} \times \sqrt{3} = \sqrt{2} \times 3 \times \sqrt{3} = 3\sqrt{6} \]
Thus, the simplified form of \( \sqrt{54} \) is \( 3\sqrt{6} \).
The answer is:
A. \( 3\sqrt{6} \)