Simplify the following expressions involving radicals and exponents: sqrt(108) + sqrt(27) - sqrt(3), (6)/(sqrt(5) - 1), and (53)2 / 54.

$$\sqrt{108} = \sqrt{36 \times 3} = \sqrt{36} \times \sqrt{3} = 6\sqrt{3}$$ $$\sqrt{27} = \sqrt{9 \times 3} = \sqrt{9} \times \sqrt{3} = 3\sqrt{3}$$

$$(6 + 3 - 1)\sqrt{3} = 8\sqrt{3}$$

The correct option is A.

$$\boxed{\text{A. } 8\sqrt{3}}$$

2. Rationalize the denominator: $\frac{6}{\sqrt{5} - 1}$

Use the difference of squares formula $(a-b)(a+b) = a^2 - b^2$ for the denominator.

$$\frac{6(\sqrt{5} + 1)}{(\sqrt{5})^2 - (1)^2}$$

$$\frac{3(\sqrt{5} + 1)}{2}$$

The correct option is B.

$$\boxed{\text{B. } 3(\sqrt{5} + 1)/2}$$

3. Simplify: $(5^3)^2 \div 5^4$}

$$5^{6-4} = 5^2$$

The correct option is A.

$$\boxed{\text{A. } 5^2}$$

4. Solve: $6^x = 216$

$$x = 3$$

The correct option is B.

$$\boxed{\text{B. } x=3}$$