Simplify. \[ \sqrt{108} \]

Simplify the expression without using a calculator. \( \log _{9} 9=\square \)

2. \( \frac{1}{\sqrt{3}+\sqrt{2}} \div \frac{1}{\sqrt{4}+\sqrt{3}} \div \frac{1}{\sqrt{5}+\sqrt{4}}= \) ?

Simplify the expression without using a calculator. \( \ln e^{2}=\square \)

20. Vereinfache im Kopf. \( \begin{array}{lll}\text { a) }\left(5^{\frac{4}{5}}\right)^{\frac{5}{2}} & \text { b) }\left(36^{\frac{3}{4}}\right)^{\frac{2}{3}} & \text { c) }\left(49^{-\frac{6}{7}}\right)^{\frac{7}{12}}\end{array} \)

Find \( \|\mathbf{v}\| \). \( \mathbf{v}=-3 \mathbf{i}+7 \mathbf{j} \) \( \begin{array}{l}\|\mathbf{v}\|=\square \\ \text { (Simplify your answer. Type an exact answer, using radicals as needed.) }\end{array} \)