(b) Write $\sqrt{45}+\sqrt{20}$ in the form $k \sqrt{5}$ (f)

Step 1 ：Write \(\sqrt{45}+\sqrt{20}\) in the form \(k \sqrt{5}\)

Step 2 ：First, simplify the square roots. We know that \(\sqrt{45}\) can be written as \(\sqrt{9*5}\) and \(\sqrt{20}\) can be written as \(\sqrt{4*5}\). This simplifies to \(3\sqrt{5}\) and \(2\sqrt{5}\) respectively.

Step 3 ：Adding these together gives \(5\sqrt{5}\).

Step 4 ：\(\boxed{5\sqrt{5}}\) is the final answer.