$C=......=\frac{3x+5\sqrt{x}-4-(\sqrt{x}+1)(\sqrt{x}-1)+(\sqrt{x}+3)^{2}}{(\sqrt{x}+3)(\sqrt{x}-1)} = \frac{3x+5\sqrt{x}-4-x+1+x+6\sqrt{x}+9}{(\sqrt{x}+3)(\sqrt{x}-1)} = \frac{3x+11\sqrt{x}+6}{(\sqrt{x}+3)(\sqrt{x}-1)} = \frac{\sqrt{x}(3\sqrt{x}+2)+3(3\sqrt{x}+2)}{(\sqrt{x}+3)(\sqrt{x}-1)} = \frac{(3\sqrt{x}+2)(\sqrt{x}+3)}{(\sqrt{x}+3)(\sqrt{x}-1)} = \frac{3\sqrt{x}+2}{\sqrt{x}-1}$