\(C=\dfrac{4}{\sqrt{5}-1}-\dfrac{10}{\sqrt{5}}+\dfrac{\sqrt{125}}{\sqrt{5}}+\sqrt{2}\sqrt{\dfrac{5}{2}}\\ =\dfrac{4\left(\sqrt{5}+1\right)}{5-1}-\dfrac{\sqrt{5}.\sqrt{5}.2}{\sqrt{5}}+\sqrt{\dfrac{125}{5}}+\dfrac{\sqrt{2}.\sqrt{5}}{\sqrt{2}}\\ =\dfrac{4\left(\sqrt{5}+1\right)}{4}-2\sqrt{5}+\sqrt{25}+\sqrt{5}\\ =\sqrt{5}+1-2\sqrt[]{5}+5+\sqrt{5}=6\)