Start with the given expression
The goal of simplifying expressions with square roots is to factor the radicand into a product of two numbers. One of these two numbers must be a perfect square. When you take the square root of this perfect square, you will get a rational number.
So let's list the factors of 54
1, 2, 3, 6, 9, 18, 27, 54
Notice how 9 is the largest perfect square, so lets factor 54 into 9*6